maarkean, is it MAF (it would say memory allocation failure) crashes or just random game shutting off. there's not much to be done for MAFS. all big mods can have them. you can try playing on lower graphics or a smaller map if thats the case.
Otherwise, is it version 2.1 or 2.8/2.85. 2.1 there may not be much to help, 2.8 or 85 I can probably fix for you. Are you playing with Choose Religions on? There was a crash with that in the 2.8s when someone founded a non default religion in one of the 4 later techs (which would be around 860AD). I can fix the XML for you if thats the case.