50 People --> Level 2
200 People --> Level 3
400 People --> Level 4
800 People --> Level 5

Level 5 is the máximum level.

you'd have to rebalance the whole progression for more levels to make any sense. it's already pretty hard to get to level 4 and almost impossible to make it to level 5 without artificially delaying the end of the game. 

hmm, with the current progression, level 6 would mean 1600 pop. if you built you cap on a 3 grain tile, you'd need more than 500 food per grain to make that even possible, and it would take hundreds of turns to get there. doesn't seem plausible. 

getting a city to level 5 as a prereq for spell victory could work, though (not necessarily the capital - i think "any city" takes long enough)

Well, I think SD is in for adjusting the level increments anyways, as level 2 happens way too soon and level 4 happens way too late. Level 5 is bear untouchable.

I propose the following:

100 People --> Level 2
200 People --> Level 3
300 People --> Level 4
400 People --> Level 5

then add:

500 People --> Level 6 -- only capital for Spell of Mastery Victory (as you receive a needed building upon this level up)

Awesome idea! So, if I understand correctly, in addition to the three buildings and extra option would be to get +1 essence. I like it!

But would be essence for the three types? Perhaps it would make more sense to give +1 essence option to Conclave, +1 grain to Town and +1 Material to fortress[/quote]

That would work, too!  I just find that some of the choices at level up don't help me as much as an extra essence would.  Especially if I have built a lot of unrest buildings in my cities already.