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Thálassa System Reference Document (v0.4.2)

Thálassa is based on Cairn SRD and is licensed under CC-BY-SA 4.0.

Thálassa is an adventure game for one facilitator (the odigós) and at least one other player. Players act as fearless explorers of the Mediterranean of the Mythical Age, studded with mysterious islands, thick forests, legendary creatures, labyrinths and dangers.



Thálassa was written with the following design philosophies in mind:


The odigós’s role is to portray the rules, situations, NPCs, and narrative clearly, while acting as a neutral arbiter.


A character’s role or skills are not limited by a single class. Instead, the equipment they carry and their experiences defines their specialty.


Characters may be powerful, but they are also vulnerable to harm in its many forms. Death is always around the corner, but it is never random or without warning.

Fiction First

Dice do not always reflect an obstacle’s difficulty or its outcome. Instead, success and failure are arbitrated by the odigós in dialogue with the players, based on in-world elements.


Characters are changed through in-world advancement, gaining new skills and abilities by surviving dangerous events and overcoming obstacles.

Player Choice

Players should always understand the reasons behind the choices they’ve made, and information about potential risks should be provided freely and frequently.


The odigós and the players each have guidelines that help foster a specific play experience defined by critical thinking, exploration, and an emergent narrative.

Shared Objectives

Players trust one another to engage with the shared setting, character goals, and party challenges. Therefore, the party is typically working together towards a common goal, as a team.

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Principles for odigoí


  • Provide useful information about the game world as the characters explore it.
  • Players do not need to roll dice to learn about their circumstances.
  • Be helpful and direct with your answers to their questions.
  • Respond honestly, describe consistently, and always let them know they can keep asking questions.


  • Default to context and realism rather than numbers and mechanics.
  • If something the players want to do is sincerely impossible, no roll will allow them to do it.
  • Is what the player describes and how they leverage the situation sensible? Let it happen.
  • Saves cover a great deal of uncertain situations and are often all that is necessary for risky actions.


  • The game world is organic, malleable and random. It intuits and makes sharp turns.
  • Use random tables and generators to develop situations, not stories or plots.
  • NPCs remember what the PCs say and do,and how they affect the world.
  • NPCs don’t want to die. Infuse their own self-interest and will to live into every personality.

Narrative Focus

  • Emergent experience of play is what matters, not math or character abilities. Give the players weapon trainers and personal quests to facilitate improvement and specialization.
  • Pay attention to the needs and wants of the players,then put realistic opportunities in their path.
  • A dagger to your throat will kill you, regardless of your expensive armor and impressive training.


  • The game world produces real risk of pain and death for the player characters.
  • Telegraph serious danger to players when it is present. The more dangerous, the more obvious.
  • Put traps in plain sight and let the players take time to figure out a solution.
  • Give players opportunities to solve problems and interact with the world.


  • A Prize is specific to the environment from where it is recovered. It suggests a story.
  • A Prize is something valuable, but non necessarily a treasure or materially valuable.
  • A Prize can be anything that calls to action the players.
  • Use the Prize as a lure to exotic locations under the protection of intimidating foes.


  • Give players a solid choice to force outcomes when the situation lulls.
  • Use binary “so, A or B?” responses when their intentions are vague.
  • Work together with this conversational progress to keep the game moving.
  • Ensure that the player character’s actions leave their mark on the game world.

Die of Fate

  • Gods are capricious: sometimes they favour the characters, other times they will play against them.
  • In these situations, roll 1d6. A roll of 4 or more generally favors the players.
  • A roll of 3 or under tends to mean bad luck for the PCs or their allies.

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Principles for Players


  • Attributes and related saves do not define your character. They are tools.
  • Don’t ask only what your character would do, ask what you would do, too.
  • Be creative with your intuition, items, and connections.


  • Seek consensus from the other players before barreling forward.
  • Stay on the same page about goals and limits, respecting each other and accomplishing more as a group than alone.


  • Asking questions and listening to detail is more useful than any stats, items, or skills you have.
  • Take the odigós’s description without suspicion, but don’t shy away from seeking more information.
  • There is no single correct way forward.


  • Treat NPCs as if they were real people, and rely on your curiosity to safely gain information and solve problems.
  • You’ll find that most people are interesting and will want to talk things through before getting violent.


  • Fighting is a choice and rarely a wise one; consider whether violence is the best way to achieve your goals.
  • Try to stack the odds in your favor and retreat when things seem unfavorable.


  • Think of ways to avoid your obstacles through reconnaissance, subtlety, and fact-finding.
  • Do some research and ask around about your objectives.


  • Set goals and use your meager means to take steps forward.
  • Expect nothing. Earn your reputation.
  • Keep things moving forward and play to see what happens.

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Principles of the World

The Sea (hē thálassa)

  • The Know World mostly faces the Sea. It is a vast basin on which peoples of different cultures live and where the creatures of myth roam free.
  • The daring and the brave venture into its waters. In distant lands they go in search of the Prize and fortune and glory.
  • The Sea is dotted with wild and unknown islands, ready to be explored and despoiled. The mainland is for the most part unexplored and mysterious.


  • Gods are real, they walk among humans. Sometimes they fall in love with them, sometimes they are envious.
  • They are powerful and capricious, but not almighty. They are immortal, but they can be injured.
  • One can appeal to the deities to request their intervention. Often they will not listen, sometimes they will respond unpredictably.

Demigods & Heroes

  • The Demigods are not necessarily the result of the union of a god and a mortal but some are, like Heracles.
  • Those who demonstrate strength, power, good family, and good behavior are termed heroes.
  • After death Gods may grant the apotheosis. When this happens the hero assumes the title of Demigod.

Deeds & Labours

  • Characters are called to action out of obligation (labours) or to seek glory (deeds). They will often cross The Sea to accomplish their duties.
  • Whether they are demigods, heroes or ordinary people, they all have something in common: Fate is inescapable. The Moirai have already established the length of their thread. They accept it and face creatures and oddities with courage.
  • Characters prefer cunning to brute force. War is not a sport, after all. However, some times they will be arrogant and overconfident. This is called hubris and is punished by circumstances and the gods.

Aoidos & Myths

  • Myths passed down in literature are real history in this world.
  • Being passed down orally by the aoidos, there are conflicting versions of the same story.
  • It is possible to meet the heroes of myth. The odigoí is free to choose which mythical era to set the adventure in.

Eukhé & Goïteia

  • When one appeals to a god, they are a eukhé (prayer). Eukhé is the high and noble form of magic.
  • In Egypt, west of Lybia, the high priests practice heka (magic) that draws on primordial power through rituals and incantations.
  • Importing some incantations, which are passed down without fully understanding their function and power, some practice goïteia, a low and limited form of magic that has lesser effects than either eukhé or heka. Practitioners of goïteia are frowned upon and considered by most to be charlatans.


  • Around the vast Sea on mysterious islands or impenetrable forests are located labyrinths.
  • There are different types of labyrinths. Some are physically mazes built to imprison and protect. Others are networks of caves or palaces with complex geometry.
  • Those who face the dangers of the labyrinths will be rewarded with Prizes and other riches.

The Underworld

  • The Underworld is a real (but hidden to the living) physical place where the souls of the dead dwell. These are only shadows of the mortal that they were, with no sense of purpose. The Underworld has a complex geography it is crossed by rivers and inhabited and defended by creatures.
  • It is possible to descend into the Underworld with the rite of katabasis. The ability to enter the realm of the dead while still alive, and to return, is a proof of being a hero. The purpose of the descent is to recover a quest-object or a loved one, or with heightened knowledge
  • It is also possible to summon the souls of the dead with the rite of nekyia. In this case the descent into the Underworld will not be physical and will have the purpose of obtaining knowledge or prophecies from the dead.

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Character Creation

Name, Origin & Traits
First, choose or roll a name for your character from the Background tables, then their profession, which informs their knowledge and potential skills, and their origin, indicating where they come from.

Next, roll for the rest of your character’s traits (appearance, speech, mannerisms, beliefs, reputation, etc.) on the Character Traits tables.

Finally, roll for their age (2d20+10).

Ability Scores

Player Characters (PCs) have just three attributes:
kratos (KRA) (strength), tekhne (TEK) (nimbleness), and thumos (THU) (control). When creating a PC, the player should roll 3d6 for each of their character’s ability scores, in order. They may then swap any two of the results.

Ines rolls for her character’s KRA, resulting in a 2, a 4, and a 6, totaling 12. The next two ability rolls result in a 9 for TEK and a 13 for THU. She decides to swap the 12 and the 9, for a character with 9 KRA, 12 TEK and 13 THU.


Roll 1d6 to determine your PC’s starting Stamina (STA), which reflects their ability to avoid damage in combat. STA does not indicate a character’s health or fortitude; nor do they lose it for very long (see Healing). If an attack takes a PC’s STA exactly to 0, the player must roll on the Scars table.


Characters have a total of inventory slots equal to their KRA: this represents the character’s ability to to bear the weight and fatigue of carrying the equipment without being adversely affected.

Most items take up one slot, and small items can be bundled together. Slots are abstract and can be rearranged per the odigós’ discretion.

Bulky items take up two slots and are typically two-handed or awkward to carry. Anyone carrying a full inventory (e.g. filling all 10 slots) is reduced to 0 STA.

A PC cannot carry more items than their inventory allows. Carts (which must be pulled with both hands), horses, or mules can increase inventory. Hirelings can also be paid to carry equipment.

Starting Gear

All PCs begin with:

  • Three days’ rations (one slot)
  • A weapon (roll on the related table)
  • 3d6 electron coins

Roll on the Starting Gear tables to determine your PC’s armor, tools, and equipment.

See the Equipment List for related armor, damage, and slot values. Smaller items can sometimes be bundled together into one slot.

Background (d20)

Female Names

1 Althea 6 Deipyle 11 Lede 16 Phylia
2 Berenike 7 Electra 12 Lyra 17 Themis
3 Chloris 8 Eunice 13 Metis 18 Thyia
4 Corythia 9 Galatea 14 Mykale 19 Xanthe
5 Deineira 10 Helike 15 Niobe 20 Zoe

Male Names

1 Agelaus 6 Croesus 11 Epistor 16 Lycoris
2 Audax 7 Damastor 12 Glycon 17 Mydon
3 Brygos 8 Demokrates 13 Hyllus 18 Pheidias
4 Chrysippos 9 Dryas 14 Icarion 19 Skiron
5 Cleonicus 10 Eleon 15 Kasos 20 Timonax

Child of

1 Alcman 6 Geleon 11 Menexinos 16 Sosimenes
2 Bacis 7 Gnipho 12 Peirithous 17 Sostias
3 Diactorides 8 Hagias 13 Phaenippos 18 Teukros
4 Eumaeus 9 Melanippos 14 Philokles 19 Thaumastus
5 Eutuches 10 Menandros 15 Priam 20 Thettalos


1 Actor 6 Lyrist 11 Poet 16 Sorcerer
2 Barber 7 Mariner 12 Priest 17 Spinner
3 Blacksmith 8 Oracle 13 Sculptor 18 Tailor
4 Farmer 9 Philosopher 14 Shepherd 19 Trader
5 Magistrate 10 Physician 15 Soldier 20 Weaver


1 Amazon 6 Child of king 11 Egyptian 16 Phoenician
2 Argive 7 Ciconian 12 Ethyopian 17 Rhodian
3 Athenian 8 Cimmerian 13 Lydian 18 Spartan
4 Child of deity 9 Cretese 14 Mycenaean 19 Thracian
5 Child of hero 10 Cypriot 15 Mysian 20 Trojan

Character Traits (d10)


1 Athletic 6 Scrawny
2 Brawny 7 Short
3 Flabby 8 Statuesque
4 Lanky 9 Stout
5 Rugged 10 Towering


1 Birthmark 6 Round
2 Dark 7 Soft
3 Elongated 8 Tanned
4 Pockmarked 9 Tattooed
5 Rosy 10 Weathered


1 Bald 6 Long
2 Braided 7 Luxurious
3 Curly 8 Oily
4 Filthy 9 Wavy
5 Frizzy 10 Wispy


1 Bony 6 Perfect
2 Broken 7 Rat-like
3 Chiseled 8 Sharp
4 Elongated 9 Square
5 Pale 10 Sunken


1 Blunt 6 Gravelly
2 Booming 7 Precise
3 Cryptic 8 Squeaky
4 Droning 9 Stuttering
5 Formal 10 Whispery


1 Antique 6 Frayed
2 Bloody 7 Frumpy
3 Elegant 8 Livery
4 Filthy 9 Rancid
5 Foreign 10 Soiled


1 Ambitious 6 Honorable
2 Cautious 7 Humble
3 Courageous 8 Merciful
4 Disciplined 9 Serene
5 Gregarious 10 Tolerant


1 Aggressive 6 Lazy
2 Bitter 7 Nervous
3 Craven 8 Rude
4 Deceitful 9 Vain
5 Greedy 10 Vengeful


1 Ambitious 6 Loafer
2 Boor 7 Oddball
3 Dangerous 8 Repulsive
4 Entertainer 9 Respected
5 Honest 10 Wise


1 Abandoned 6 Defrauded
2 Addicted 7 Demoted
3 Blackmailed 8 Discredited
4 Condemned 9 Disowned
5 Cursed 10 Exiled

Starting Gear

Armor (d20)

1-3 4-14 15-19 20
None Fur Coat Linothorax Breastplate

Helmets & Shields (d20)

1-13 14-16 17-19 20
None Krános (Helmet) Aspis (Shield) Krános & Aspis

Weapons (d20)

1-5 6-14 15-19 20
Kopis (curved knife) Doru (spear), Xiphos (sword) Akontia (javelin), Sfendonai (sling) Xyston (long lance), Toxa (bow)

Expeditionary Gear (d12)

1 Cart (+4 slots, bulky) 7 Lockpicks
2 Chain (10ft) 8 Pick
3 Dowsing Rod 9 Pole (10ft)
4 Fire Oil 10 Rope (25ft)
5 Large Sack 11 Torch
6 Large Trap 12 Waterskin

Tools (d10)

1 Bellows 6 Drill (Manual)
2 Bucket 7 Fishing Rod
3 Chalk 8 Flint & Steel
4 Chisel 9 Grease
5 Cook Pots 10 Staff

Trinkets (d10)

1 Amulet 6 Lyre
2 Bottle 7 Necklace
3 Copper 8 Silver Mirror
4 Horn 9 Talisman
5 Incense 10 Tunic

Bonus Item (d20, roll on table indicated)

1-5 6-13 14-17 18-20
Tool or Trinket Expeditionary Gear Armor or Weapon Incantation

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Equipment List (Prices in Electrum)


Aspis (+1 Armor) 10
Krános (+1 Armor) 10
Fur Coat (+1 Armor) 15
Linothorax (2 Armor, bulky) 40
Breastplate (3 Armor, bulky) 60


Kopis (d6 damage) 5
Doru, Xiphos (d8 damage) 10
Akontia, Xyston (d10 damage, bulky) 20
Sfendonai 5
Toxa (d6 damage, bulky) 20

Gear & Tools

Bucket 5 Mirror 5
Cart (+4 slots, bulky) 30 Mule (+6 slots, slow) 30
Chain (10ft) 10 Net 10
Chisel 5 Oilskin Bag 5
Cook Pots 10 Pick 10
Drill (Manual) 10 Pole (10ft) 5
Fire Oil 10 Stylus & Tablet 10
Fishing Rod 10 Rations (three day’s worth) 10
Grease 10 Rope (25ft) 5
Horn 10 Saw 5
Horse (+4 slots) 75 Sack 5
Incense 10 Shovel 5
Lantern & Oil 10 Soap 1
Large Trap 20 Spike 1
Large Sponge 5 Spiked Boots 5
Lens 10 Tar 10
Lockpicks 25 Tent (fits 2 people, bulky) 20
Metal File 5 Torch 1

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Each of the three abilities are used in different circumstances (see saves, below).

Kratos (KRA): Used for saves requiring physical power, like lifting gates, bending bars, resisting poison, etc.

Kinesis (TEK): Used for saves requiring poise, speed, and reflexes like dodging, climbing, sneaking, balancing, etc.

Kanonas (THU): Used for saves to persuade, deceive, interrogate, intimidate, charm, provoke, recite incantations, etc.

A save is a roll to avoid bad outcomes from risky choices and circumstances. PCs roll a d20 for an appropriate ability score. If they roll_equal to or under that ability score_, they pass. Otherwise, they fail. A 1 is always a success, and a 20 is always a failure.

Example: Althea encounters a group of wild harpies standing guard before a tunnel entrance. Her player carefully plots a course, recognizing that her 13 TEK makes sneaking past the guards the best option. She rolls a d20, and resulting in a 10 – a success!

Deprivation & Fatigue
A PC deprived of a crucial need (such as food or rest) is unable to recover STA or ability scores. Anyone deprived for more than a day adds Fatigue to their inventory, one for each day. Each Fatigue occupies one slot and lasts until they are able to recuperate (such as a full night’s rest in a safe spot).

Resting for a few moments and having a drink of water restores lost STA but leaves the party exposed. Ability loss can usually be restored with a week’s rest facilitated by a healer or other appropriate source of expertise. Some of these services may be free, while more expedient or magical means of recovery may come at a cost.

Before calculating damage to STA, subtract the target’s Armor value from the result of damage rolls. Shields and similar armor provides a bonus defense (e.g. +1 Armor), but only while the item is held or worn.
No one can have more than 3 Armor.
Shields, gauntlets, and helms may provide additional benefits according to their use.

When the PCs encounter an NPC whose reaction to the party is not obvious, the odigós may roll 2d6 and consult the following table:

2 3-5 6-8 9-11 12
Hostile Wary Curious Kind Helpful

Enemies must pass a THU save to avoid fleeing when they take their first casualty and again when they lose half their number. Some groups may use their leader’s THU in place of their own. Lone foes must save when they’re reduced to 0 STA. Morale does not affect PCs.

PCs can hire hirelings to aid them in their expeditions. To create a hireling, roll 3d6 for each ability score, then give them 1d6 STA and a simple weapon (d6), then roll on the Character Creation tables to further flesh them out. Hirelings cost between 1-3ec per day, or a share of whatever treasure the party obtains.

Wealth & Treasure
The most common coin is the electrum (e), which is equal to 10 silver (s) and 100 copper (c).

Treasure is highly valuable, usually bulky, and rarely useful beyond its value. It can be a lure, taking PCs to exotic and even dangerous locations, and is often under the protection of intimidating foes.

Villages,strongholds, and ports of call barter and trade based on the local rarity and value of an item or commodity.

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In the world of Thálassa there are two kinds of magic: Eukhé is the invocation of divine powers and Goïteia is reciting incantations.

Everyone may use magic and Thumos is the power source. Each time an incantation, invocation, curse or divination is casted, the magic-user consumes THU equal to 1d6 points. This determines the current level of THU until recovered (the same rule for STA in Healing do apply).


Eukhé is the highest form of magic. It consists of a set of magical practices performed to evoke Gods in order to see them or know them or in order to influence them or ask them a blessing. It is a power higher than all human wisdom embracing the blessings of divination, the purifying powers of initiation and all the operations of divine possession.

The practitioner evokes the God competent for a specific domain on which he wants to have effect:

  • Apollo: divination and healing.
  • Ares: might in battle.
  • Artemis: protection in the night and charms in the hunt.
  • Aphrodite: love charms and potions.
  • Athena: insights and strategy.
  • Hermes: thievery and trickery.
  • Hephaestus: blessing weapons and armors.
  • Hera: blessing marital unions.
  • Persephone: calling upon the souls of the dead.
  • Poseidon: control over sea and weather

A time of recollection and concentration is required to appeal to the deity, equal to 1d6 turns. Then roll 1d20: if the result is 16+, the deity hears and grants the request. In any case the practice will consume THU like any other magic.


Goïteia is the lowest form of magic, including astrology, alchemy and other forms of esoteric knowledge and not well regarded in Ellas. It originated in Egypt where the high priests drew on primal power with heka. Over the centuries they have written precise forms, in the form of incantations, to evoke this form of energy. This knowledge was taken away and vulgarized by some outcast priests and then exported to foreign peoples. The incantations thus handed down are limited in number and power and their effects constrained by the precise wording.

A scroll contain a single incantations and take up one slot. They cannot be created nor transcribed, but can be recovered from places like labyrinths. If the PC is deprived or in danger, the odigós may require a PC to make a save against THU to avoid any ill-effects from reciting the incantation. Consequences of failure are on par with the intended effect, and may result in added Fatigue, the destruction of the Spellbook, injury, and even death.

Alternatively, it is possible to memorize the content of the scroll to avoid slots consumption. In this case, the practitioner takes 1 day to memorize the incantation and then they burn the scroll. Save against THU, failing results in the loss of the spell and the need to find another copy.

30 Incantations

1. Assistant Daimon: A guardian spirit stays with the target for one day. +3 to each save against THU.

2. Attraction: The target is incredibly attracted to the person reciting the spell. The reaction is automatically helpful.

3. Bind Lover: This spell permanently binds the target to the practitioner. But beware: love can also bring jealousy.

4. Bonds Release: It nullifies any bond (of loyalty, love, friendship, etc) between two people. The effect is permanent.

5. Break Enchantment: It breaks the effects of a charm, whether it be the result of eukhé or goïteia.

6. Causing Separation: A permanent curse that allows to physically divide two objects.

7. Charm Beasts: It enslaves beasts and non-rational creatures to the practitioner for 2d6 turns.

8. Coerce: Forces a sentient creature or human to respond to the practitioner’s command. Lasts 3 turns.

9. Consecration: Gives a temporary boost to KRA or TEK of +3 for 1d6 turns.

10. Direct Vision: It allows clairvoyance on a specific object, person or place for only one time per cast.

11. Dissolve Incantations: It breaks the effects of any incantation casted with goïteia.

12. Dream Revelations: It should be performed before bedtime, focusing the request on a specific subject. During the night a dream will reveal details on it. There is a 1-in-6 chance that the dream will be forgotten upon awakening.

13. Foreknowledge: The practitioner will be able to predict the future on a specific event he focuses on while reciting the incantation. It can only be attempted once per event.

14. Gain Friendship: It automatically makes friends of the target permanently.

15. Gaining Favor: The target becomes well disposed towards the practitioner. The effect lasts 1d6 days, after which his disposition may change (reaction roll).

16. Healing: It allows immediate and total recovery of stamina.

17. Induce Insomnia : This curse causes a state of insomnia to the victim, which prevents him from resting and healing properly. For the effect roll 1d6: 1-2: 3 days 3-4: 1 week, 5: 2 weeks, 6: permanent.

18. Inflict Harm: It deals 1d6 direct damage to the target.

19. Invisibility: The target becomes completely invisible for 1d6 turns. The effect does not extend to weapons and equipment.

20. Protection: Subtract 1d6 damage for the next 3 turns.

21. Questioning Corpses: Makes it possible to interrogate a human or creature corpse if it has been dead for less than a week. The target will respond as if it were alive (not bound to the truth).

22. Restrain Anger: It instantly appeases any target blinded by anger.

23. Revelation: The practitioner receives an insight into something that was not previously clear or known.

24. Separate People: A permanent curse that allows to physically divide two people forever.

25. Shadow Control: The practitioner gains control of the target’s shadow (e.g., to spy on it). It can only be cast once per target and the duration is at the practitioner’s discretion.

26. Silence: This curse deprives you of the ability to speak or make sounds of any kind for 1d6 turns.

27. Slander: This curse causes a slander to be believed to be true by anyone. The effect is permanent.

28. Sleep Talk: It can only be cast on a person who is already asleep and will force them to talk in their sleep. The person can be questioned and will have to tell the truth.

29. Subjugate: The target is completely enslaved to the practitioner’s will until released. It only works with humans.

30. Victory: It guarantees automatic victory in a fight. It is valid only once per fight against one opponent.

Amulets & Talisman

An amulet is an object believed to confer protection upon its possessor. Also a talisman is any object intended to protect, heal, or harm individuals for whom they are made, but a key difference is in their form and materiality, with talismans often taking the form of objects like clothing, weaponry, or parchment inscribed with magic texts. Some examples of function are:

  • Demon Protection
  • Restraining Seal
  • Phylactery
  • Ring for success and favor and victory.


Gifts are items imbued with a divine power. Gifts, usually granted by Gods, are powerful but have a limited and precise use. A few examples:

Achilleus’ Armor created by Hephaestus, it is impenetrable.

Aegis, the shield of Zeus which was often guarded by Athena along with his magical armour, Perseus used this when decapitating Medusa, it bore the head of Medusa to scare the enemy.

Apollon’s Bow: inducing health or death.

Caduceus: a staff used by Hermes, entwined by two serpents. Also known as the staff of healing.

Cornucopia: the horn of the river god Achelous overflowing with food.

Eros’s Bow: it generates arrows which caused the target to hate or love the first person in sight.

Harpe: a combination of a sword and sickle, and a term used to refer to the sword used by Perseus to kill Medusa, and to the sickle used by Cronus to castrate Ouranus.

The Helmet of Darkness: also known as helmet or Cap of Invisibility, was a headgear created by the Cyclopes for Hades (Pluto).

Heracles’s Bow: it belonged to the demi-god Heracles, with arrows tipped with the Hydra’s poison.

Hide of the Nemean Lion: earned by Heracles, it was impenetrable, at least by conventional weapons.

Poseidon’s Trident: Poseidon’s trademark weapon and symbol of power. The trident is imbued with the power to control and command the sea, it can also create huge tidal waves and make hurricanes.

Shield of Achilleus: used during Achille’s fight with Hector.

Shirt of Nessus: shirt poisoned with Nessus tainted/poisoned blood, used to poison and kill Heracles.

Spear of Achilleus: forged by Hephaestus and given to Peleus.

Sword of Peleus: magic sword which makes the wielder emerge victorious in battle.

Winged Helmet: winged helmet wore by Hermes.

Winged Sandals: wore by Hermes, allowing the god to fly.

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The game typically plays without strict time accounting. In a fight or circumstance where timing is helpful, use rounds to keep track of when something occurs. A round is roughly ten seconds of in-game time and is comprised of turns.

On their turn, a character may move up to 40ft and take up to one action. This may be _casting an incantation, attacking, making a second move, or some other reasonable action.

Each round, the PCs declare what they are doing before dice are rolled. If a character attempts something risky, the odigós calls for a save for appropriate players or NPCs. All actions, attacks, and movements take place simultaneously.

The odigós will telegraph the most likely actions taken by NPCs or monsters. At the start of combat, each PC must make a TEK save to act before their opponents.

Example: Althea has accidentally stumbled onto the stomping grounds of a massive Cyclop. In order to make a move before the Cyclop, she makes a TEK save. She fails, and the Cyclop gets to attack first.

Attacking & Damage
The attacker rolls their weapon die and subtracts the target’s armor, then deals the remaining total to their opponent’s STA. Unarmed attacks always do 1d4 damage.

Example: The Cyclop roars, swinging its club at Althea, who has 5 STA. The club does 1d10 damage and the odigós rolls a 4. They subtract 1 to account for Althea’s leather armor, leaving Althea with 2 STA remaining.

Multiple Attackers
If multiple attackers target the same foe, roll all damage dice and keep the single highest result.

Attack Modifiers
If fighting from a position of weakness (such as through cover or with bound hands), the attack is impaired and the attacker must roll 1d4 damage_regardless_of the attacks damage die.

If fighting from a position of advantage (such as against a helpless foe or through a daring maneuver), the attack is enhanced , allowing the attacker to roll 1d12 damage instead of their normal die.

Dual Weapons
If attacking with two weapons at the same time, roll both damage dice and keep the single highest result.

Attacks with the blast quality affect all targets in the noted area, rolling separately for each affected character. Blast refers to anything from explosions to huge cleaving onslaughts to the impact of a meteorite. If unsure how many targets can be affected, roll the related damage die for a result.

When damage to a PC reduces their STA to exactly 0, they are sometimes changed irrevocably. See the Scars for more.

Critical Damage
Damage that reduces a target’s STA below zero decreases a target’s KRA by the amount remaining. They must then make a KRA save to avoid critical damage. Additionally, some enemies will have special abilities or effects that are triggered when their target fails a critical damage save.

Any PC that suffers critical damage cannot do anything but crawl weakly, grasping for life. If given aid and rest, they will stabilize. If left untreated, they die within the hour.

Ability Score Loss
If a PC’s KRA is reduced to 0, they die. If their TEK is reduced to 0, they are paralyzed. If their THU is reduced to 0, they are delirious. Complete TEK and THU loss renders the character unable to act until they are restored through extended rest or by extraordinary means.

Unconsciousness & Death
When a character dies, the player is free to create a new character or take control of a hireling. They immediately join the party in order to reduce downtime.

Large groups of similar combatants fighting together are treated as a single detachment. When a detachment takes critical damage, it is routed or significantly weakened. When it reaches 0 KRA, it is destroyed.

Attacks against detachments by individuals are impaired (excluding blast damage).
Attacks against individuals by detachments are enhanced and deal blast damage.

Running away from a dire situation always requires a successful TEK save, as well as a safe destination to run to.

When an attack reduces a PC’s STA to exactly 0, they are uniquely impacted. Look up the result on the table below based on the total damage taken:

1 Lasting Scar: Roll 1d6 | 1: Neck, 2: Hands, 3: Eye, 4: Chest, 5: Legs, 6: Ear. Roll 1d6. If the total is higher than your max STA, take the new result.
2 Rattling Blow: You’re disoriented and shaken. Describe how you refocus. Roll 1d6. If the total is higher than your max STA, take the new result.
3 Walloped: You’re sent flying and land flat on your face, winded. You are deprived until you rest for a few hours. Then, roll 1d6. Add that amount to your max STA.
4 Broken Limb: Roll 1d6 | 1-2: Leg, 3-4: Arm, 5: Rib, 6: Skull. Once mended, roll 2d6. If the total is higher than your max STA, take the new result.
5 Diseased: You’re afflicted with a gross, uncomfortable infection. When you get over it, roll 2d6. If the total is higher than your max STA, take the new result.
6 Reorienting Head Wound: Roll 1d6 | 1-2: KRA, 3-4: TEK, 5-6: THU. Roll 3d6. If the total is higher than your current ability score, take the new result.
7 Hamstrung: You can barely move until you get serious help and rest. After recovery, roll 3d6. If the total is higher than your max TEK, take the new result.
8 Deafened: You cannot hear anything until you find extraordinary aid. Regardless, make a THU save. If you pass, increase your max THU by 1d4.
9 Re-brained: Some hidden part of your psyche is knocked loose. Roll 3d6. If the total is higher than your max THU, take the new result.
10 Sundered: An appendage is torn off, crippled or useless. The odigós will tell you which. Then, make a THU save. If you pass, increase your max THU by 1d6.
11 Mortal Wound: You are deprived and out of action. You die in one hour unless healed. Upon recovery, roll 2d6. Take the new result as your max STA.
12 Doomed: Death seemed ever so close, but somehow you survived. If your next save against critical damage is a fail, you die horribly. If you pass, roll 3d6. If the total is higher than your max STA, take the new result.

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Creating Monsters

Use the following template to model any more sophisticated Monster or NPC:

Name X STA, X Armor, X KRA, X TEK, X THU, Weapon (dX, special items, qualities)

  • Engaging descriptor of appearance or demeanor
  • Quirk, tactic, or peculiarity making this NPC unique
  • Special effect or critical damage consequence

General Principles
Ability Scores: 3 is deficient, 6 is weak, 10 is average, 14 is noteworthy, and 18 is legendary. Adjust as necessary.

  • Give average creatures 3 STA, give hardy ones 6 STA, and serious threats get 10+ STA.
  • Use flavor and style to help them stand out. Players will remember a pig-faced humanoid looking for his missing sheep more easily than a generic goblin archer.
  • Use critical damage to lean into the threat or strangeness of any aggressive NPC.
  • Remember that STA is Hit Protection , not Hit Points. It’s a measure of resilience, luck, and gumption - not health.

Converting from OSR Games

  • Give 1 STA per HD for most creatures.
  • Most humanoids have at least 4HP.
  • Morale can also be used as a baseline.

Some pointers:

  • Is it good at avoiding a hit? Give it STA.
  • Does it soak up damage? Give it Armor.
  • Is it strong? Give it a high KRA.
  • Is it nimble? Give it high TEK.
  • Is it charismatic? Give it high THU.

Damage die are roughly the same, though armed attacks do at least 1d6 damage.

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Rules Summary

On their turn, a character may move up to 40ft and take up to one action. Actions may include casting an incantation, attacking, making a second move, or other reasonable activities. Actions, attacks, and movements take place simultaneously. Whenever turn order is uncertain, the PCs should make a TEK save to see if they go before their enemies.

Retreating from a dangerous situation always requires a successful TEK save, as well as a safe destination to run to.

KRA: Brawn, prowess & resistance.
TEK: Dodging, sneaking & reflexes.
THU: Persuasion, intimidation & magic.


  • Roll a d20 equal to or under an ability.
  • 1 is always a success, 20 is always a failure.

STA indicates a PC’s ability to avoid getting hurt. It is lost during combat & recovered after a few moment’s rest.

PCs have 10 inventory slots: four on their body and six in their backpack (which acts as a sleeping bag if emptied). Most items take up a one slot, but smaller items can be bundled. Bulky items take up two slots and are awkward or difficult to carry.

Filling all ten item slots reduces a PC to 0 STA. PCs cannot carry more than their inventory allows, though carts & horses may provide an increase in slots.

Deprived PCs cannot recover STA. If deprived for more than a day,they add a Fatigue to inventory. Fatigue occupies one slot and lasts until they can recover in safety. This effect is cumulative.

A moment’s rest and a swig of water will restore lost STA, but may leave the party vulnerable. Ability loss requires a week’s rest and the aid of a skilled healer.


The attacker rolls their weapon die and subtracts the target’s Armor, then deals the remaining total to their opponent’s STA.

Before calculating damage to STA, subtract the target’s Armor value from the result of damage rolls. Shields and similar armor provides a bonus defense (e.g. +1 Armor), but only while the item is held or worn.

No one can have more than 3 Armor.

Unarmed attacks always do 1d4 damage. If multiple attackers target the same foe, roll all damaged ice and keep the single highest result. If attacking with two weapons at the same time, roll both damage dice and keep the highest.

If an attack is impaired , the damage die is reduced to 1d4, regardless of weapon. If the attack is enhanced , the attacker rolls 1d12. Attacks with the blast quality affect all area targets, rolling separately for each.

If an attack takes a PC’s STA exactly to 0, the player rolls on the Scars table.

Damage that reduces a target’s STA below 0 decreases their KRA by the remainder. They must then make a KRA save to avoid critical damage. Failure takes them out of combat, dying if left untreated.

Having KRA 0 means death; having TEK 0 is paralysis; having THU 0 is delirium.

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Credits and Acknowledgements

Thálassa is based on the Cairn SRD by Yochai Gal (release under CC BY-SA 4.0 license) which derived from Weird North by Jim Parkin, Into the Odd by Chris McDowall, and Knave by Ben Milton.

A huge thanks to:

  • Yochai Gal: for Cairn, the NSR Discord server, and the kind support.
  • Tom Van Winkle: for correcting all the Greek words and addressing me on magic in the ancient world.
  • Alessio Persichetti: for all the valuable advice and for tolerating my lucubrations
  • The NSR and The Cauldron communities: for advice and support on this project

I dedicate as always this work to my wife Cristina. Thanks for giving up some of your time with me.


  • v 0.4.2: added Credits and Acknowledgements
  • v 0.4.1: fixed the index
  • v 0.4: first public release, completed Magic with Goïteia and Incantations
  • v 0.3: added Principles of the World, completed backgrounds, change magic terminology, completed Eukhé
  • v 0.2: drafted Magic, completed equipment, changed attributes terminology, added Gifts
  • v 0.1: forked Cairn, modified encumbrance rules, replaced Treasure with Prize