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Cthulhu Eternal - Medieval SRD

Suggested Price $0.50

“I recalled forcibly the events preceding my confinement and seclusion in this veritable medieval fortress.
They were not pleasant, and I shuddered anew when I remembered ...”


IMPORTANT NOTE: This PDF contains the text of a full set of rules for a (setting-independent) RPG which embraces Lovecraftian adventures in the Medieval times. In OGL terms it is a “System Reference Document” (or SRD). While the rules contained in this PDF give you everything that you’d need to run a game they are not illustrated, typeset, or furnished with detailed examples as you would expect from a core RPG rulebook. Neither do they describe a particular game world, with a set of monsters, rituals, tomes and the like (although guidelines for building and encountering such elements are fully described).

Cthulhu Eternal is a multi-era, setting agnostic ruleset which aims to support inventive game designers who have original ideas for Lovecraftian roleplaying games or scenarios. It draws upon the long line of D100 games of Cthulhu-themed investigation, offering a beautifully streamlined and elegant set of mechanics to support a diverse range of gaming styles.

Different eras of human history each have their own flavor and character – due in part to the technology available, and in part due to social conventions of the day. Recognizing this, Cthulhu Eternal exists as a family of inter-related rules engines – each based on the same mechanics but tailored to the needs of a specific era.

This version of Cthulhu Eternal is specially designed to support Lovecraftian games set in Europe during Medieval times (approximately 800CE to 1300CE).While the Medieval period is not one typically associated with investigative horror, many of the common themes of cosmic horror resonate strongly with the vast social and cultural changes that sweep through Europe during these centuries. Science and rational conceptions of the world are luxuries for a future age -- in these times the hidden horrors exist as an unknowable cancer. Something inexorably nibbling away at the institutions that keep men safe and sane.

The church, trust in the natural order of the world, and established feudal traditions of social order ... all of them are as a speck of dust when the alien forces of the Cthulhu Mythos choose to rouse. The only thing that stands between mankind and a horrific awakening of ancient terrors ... is a few hardy Protagonists willing to stand against impossible odds. Because the consequences of not fighting the horrors is something even more terrifying.

The Cthulhu Eternal Medieval SRD aims to support a broad spectrum of different types of Lovecraftian game set during the Medieval period. Whether you want a gritty and historical tone or something more pulpy and fantasy inspired, these rules give you the building blocks to tailor a memorable and evocative Medieval tale of dread. Whether it's a tense and closeted murder mystery within the confined walls of a draughty monastery, or an action packed chase to stop Yog-Sothoth manifesting above the frozen waters of the Thames, these rules have everything you need.

Other versions of Cthulhu Eternal currently available in SRD form:

Each of these rulesets can be paired with the Open Cthulhu Mythos SRD, which has compatible game stats for all Lovecraft's most famous creations.

More titles are planned as future releases.

Contained within the 100+ page PDF, you will find rules covering the following topics:

Part 1: Rules of the Game

  • 1.0          Core Game Concepts
  • 2.0          Creating Protagonists (the term given to player characters in Cthulhu Eternal)
  • 3.0          The Game (skills, tests, willpower)
  • 4.0          Combat
  • 5.0          Equipment
  • 6.0          Vehicles
  • 7.0          Sanity
  • 8.0          Downtime (developing protagonists between adventures)

Part 2: Game Moderator Resources

  • 9.0          Maddening Revelations
  • 10.0        Supernatural Effects

Part 3: Game Building Resources

  • 11.0       Designing New Archetypes
  • 12.0       Translating Creatures from D100 Games
  • 13.0       Gumshoe Creature Conversion

For convenience, this pack also includes two versions of the Cthulhu Eternal Cold War Day character sheet. One is a high-resolution non-fillable PDF, suitable for printing. The other is a fillable PDF sheet which will ONLY work with the full version of Adobe Reader – save the file to a local drive and open it using the Adobe Reader App (using it in-browser or on mobile devices won’t work).

12_Eternal_Char_Sheet_Medieval_-_Front_a Character Sheet Back


We are releasing this SRD to support community creators who would like to produce their own original Lovecraftian RPG creations, but who need a free and open set of rules to serve as a foundation to their own creative endeavors. As such, there are no real limitations on what you can do with this material (other than those described in the Open Game License).

Some examples of ways this SRD could be used:

  • Do you have some old Lovecraftian scenarios sitting around gathering dust for want of a free and open game system to use in their publication? Why not convert the scenario to work with Cthulhu Eternal, release them and direct readers to download this SRD to run them? Or even talk to us about bundling the SRD with the scenario PDF itself?
  • Do you have a fantastic idea for an innovative Lovecraftian game but the thought of having to re-create all the “nuts and bolts” of a game system is a distraction from your high concept? Well, you could always recycle some or all of the mechanics in this SRD to be those “nuts and bolts.” Because the material is virtually 100% open content, you can copy/paste whatever rules you want into your original creation (as long as you release under the OGL and credit us as per the requirements of the license).

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Reviews (0)
Discussions (5)
Customer avatar
Robert H May 27, 2023 11:18 pm UTC
I've noticed that shields are great if you're attacked by more than one foe, but if two warriors face off - one with shield and one without, each making one attack a round, the shield doesn't do its user much good as they will use their weapon attack as their parry and that's all they need. Is that correct?
Customer avatar
Dean E May 28, 2023 12:12 am UTC
Yes, that's right. We wanted to keep the combat rules fairly streamlined while adding some benefits from having a shield when fighting up close. One alternative we considered (and which you are welcome to use instead) is that shields add BOTH a +1 or +2 to Armor AND allow a number of free parry attempts per turn.
Customer avatar
Robert H May 28, 2023 12:15 am UTC
Customer avatar
Robert H May 20, 2023 4:38 pm UTC
A question, Breaking Point is SAN minus POW, and occurs when SAN drops to it.

How does this combine with changes to SAN either losses or gains, is Breaking Point moving/readjusted (if so how does SAN drop to it), or is it fixed from initial SAN, and if so is that "Current SAN" or "Recovery SAN"
Customer avatar
Dean E May 21, 2023 12:08 am UTC
Breaking Point (BP) is initially set at a Protagonist's starting SAN minus their POW. The BP doesn't change when SAN is lost or gained *except* where a SAN loss would bring the current SAN equal to or below the BP. That's when the Protagonist has hit their Breaking Point, and usually gains a mental disorder of some type. When that happens a NEW Breaking Point is calculated -- that is their current SAN (post loss) minus POW.

So, for example, if a Protagonist has a POW of 10, they would usually start with SAN of 50 and a BP of 40. If they lose four points in small encounters with the Mythos, they would have a SAN of 46 and still have a BP of 40. If they then have a major encounter and lose 7 SAN in one go, their SAN total would drop to 39 -- below their Breaking Point. They would develop a Disorder and also reset the Breaking Point to their current SAN (39) minus POW (10) ... so, a new BP of 29. Even if their SAN goes back up over the old Breaking Point, that new BP stays unchanged. Hence BP changes...See more
Customer avatar
Robert H May 21, 2023 12:19 am UTC
Thank you for the very prompt reply.
Customer avatar
Robert H May 13, 2023 10:45 pm UTC
The fillable character sheet PDF seems a bit wonky. It works fine but upload it to dropbox and you can't see it online, only download it, and I find programs I can export a PDF into also don't like it.

The non-fillable character sheet has none of that issue.
Customer avatar
Dean E May 13, 2023 11:20 pm UTC
Yes, the fillable sheets will ONLY work with full versions of Adobe Reader (not the cut-down version that allows PDFs to be viewed in a browser window etc). This is a limitation of Adobe's software, so sadly nothing we can easily get around without ditching all the nifty interactive buttons on the sheet.
Customer avatar
Robert H May 20, 2023 4:57 pm UTC
Thanks, and I do like the nifty interactive buttons.
Customer avatar
Robert H May 12, 2023 11:49 pm UTC
What would be the best source for bestiary to convert - ordinary animals such as wolves, bears, hounds and horses including warhorses, palfreys etc?
Customer avatar
Dean E May 13, 2023 8:38 am UTC
I imagine there are several possible places to look for D100 stats for mundane creatures, but my normal go-to resource is Mongoose's "Monsters of Legend" -- a supplement for the Legend RPG.

That book has about 20-25 mundane creatures (including wolves, horses, hawks, bears, etc) along with a wealth of common fantasy, mythological, and traditional horror monsters. Best of all, though, the whole book (minus art) is Open Game Content under the OGL, so is free to remix and adapt for personal or commercial use.
Customer avatar
Chad B May 13, 2023 12:53 pm UTC
I'd also give the Myrhras books a look. They have quite a few mundane animals.
Customer avatar
Dean E May 13, 2023 2:15 pm UTC
I would also second this suggestion -- the good folks who publish the Mythras system (core rules at: have repackaged a lot of the older D100 stat blocks. The main Mythras book is an absolute steal for what you get.
Customer avatar
Andrew E May 03, 2023 12:12 am UTC
My brain went straight to Evil Dead: Army of Darkness. Thanks for making this available
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File Last Updated:
May 05, 2023
This title was added to our catalog on April 30, 2023.