I haven't uploaded something to these forums in years, but here is the Forever Dark Ages Mod(comp). The main effect in this mod is the random loss of knowledge over the course of the game. The algorithm is that every turn a random technology from the entire tech-tree is selected. If this technology has already been research, then it will be deleted from your resarch history and all knowledge of the technology will be erased. Eventually you will reach a point where the rate of research is equal to the rate of forgetting technology (often the Medieval Era). At first glace this may seem annoying, but it runs smoothly. Units or buildings that require a forgotten technology will be put on hold until that technology is re-researched. Effectively, your progress up the technology tree is not measured by cumulative research power but rather by current research power. Now, you can truly knock an opponent back to the Stone Age. An indirect effect is the emphasis on military conquest (just like the European Dark Ages). Militaristic expansion is both caused by the lack of adancement (available buildings have already been constructed) and is a means of advancing (more cities => more research power => greater research power). A second effect is that the rich get richer; more advanced civilizations have more means by which to enhance their research output and again advance more. This is doubly true because of the highly militaristic aspect of the game. Potential Addition: Because the most powerful army can take over the world piece by piece (advancing technologically with each step) creating a "Holy War" or pitting all other civilizations against this one, could add an interesting game mechanic. Potential Addition: A revised calendar system. Stretching the calender from 300AD to 1500AD at a constant rate of years/turn should be effective and realistic. Annoying bit: while the Granary can be put on hold if Pottery is forgotten, to be completed at another time, unfinished World Wonders are dimantled and converted into Gold. This is potentially annoying. Usually I am not a builder so it has not bothered me yet. Here is the sum of the added code, in the python CvEventManager, onBeginGameTurn Code: for iPlayer in range(gc.getMAX_PLAYERS()): pPlayer = gc.getPlayer(iPlayer) pTeam = gc.getTeam(pPlayer.getTeam()) rTech = CyGame().getSorenRandNum(gc.getNumTechInfos(), "Lost Tech") if (iPlayer == 0) and (pTeam.isHasTech(rTech) == 1) : CyInterface().addImmediateMessage("Technology has been Lost", "AS2D_NEW_ERA") pTeam.setHasTech(rTech, 0, iPlayer, 0, 0) iResearch = (0 - pTeam.getResearchProgress(rTech)) pTeam.changeResearchProgress(rTech, iResearch, iPlayer) This mod(comp) was initially intended to be a step toward creating a perpetual mod, where civilization could rise and fall in all manners (technologically, geographically, and culturally). Most of my playtesting was done under normal gamespeed, with tech-trading turned off (for obvious reasons), and an agressive AI. I played at my normal difficulty and got wiped off the earth within 100 turns a couple of times.