The only civ which may pass and found cities on Mountains are Incas. I think it may be justified game-wise but this is highly unrealistic. I think a better solution would be to make it to work like in Civ IV - Caveman2Cosmos: there are a tech (Mountaineering?) and a promotion which make it possible to pass mountains and place improvements on them and there is some other tech which makes it possible to found a city on a mountain. So my suggestions are: - Incas have an immediate, full access to mountains (maybe they should get some extra bonus) - some tech from late Renaissance makes it possible to enter and place improvements on mountains (road/railroad, mine/quarry) for the other civs - some tech from early Industrial Era makes it possible to found cities on mountains for the other civs - mountains may contain resources and bonuses. In this way after some tech all land tiles may be fully usable for all civs. S.