Ecofarm
Deity
If all you did was require masonry, you'd balance it pretty majorly. 30 turns into the game, that +2 production doesn't have nearly the effect it would otherwise have.
And casting it with 3 cities is arguably (?) a stronger strat... but who wants to tech masonry instead of education and mysticism or bronze??
Maybe you do it after and cast turn 80 (without a religion)... that's a hard nerf.
quickspeed