corpses = pollution is a bit much IMO.
so is 50 turns for them to decompose, a year or five and only scraps should
remain!
hmm. 10 turns, then 5% every turn of rising up...no chance they are gonna take decomp lying down. They will rise eventually.
I also like to see a wonder (black piramid?) that does what Nagash did: kill all humans in his kingdom and raise them as undead.
It should be a fairly difficult thing to build, but the rewards would be high:
-no more food needed.
-Plus free raise dead spell/turn or -free 5 free lichlord units (for raising dead).
Hmm population growth could come from 'harvesting' those corpse fields.
(All undead units can disband in necropolis to add 1 pop)
or from 'mining' graveyard enhanced squares, bones/skulls would replace shoves of grain.
Could a wonder replace all irrigation/hamlet with graveyard enhancements?
edit:
Maybe if chance of a corpsepile can be kept relatively low, you can cleanup a tile by burrying them, creating a graveyard. (no chance of undead rising spontaneously, unless by winds-of-magic.)
This has no value for most civs appart from +

maybe or -

.... But for undead civs these would be great attractors.
Graveyards can be cleared by workers at the same rate as clearing a forest. But with a chance of 10% of barbarian undead rising.
If dead rising spontaneously % could be tied in with warpstone or other souces of magic being nearby, that would be realistic. but much trouble for something that could be a rare occurence. Unless people start fichting for a chunk of green glowy stuff.
-technical question: can terrain appearance be changed according to culture? (Undead fields / chaos plains / bleak forrests etc)