Huge cities... huge problem

[Poulp']

ah... the gladiator's revolt... so many good memories, there's nothing like the smell of a burning city in the early morning while pretorians are fighting on the walls trying to get Spartacus...

What Guyus Germanicus said is true, one should always be wary of what kind of army can pop up.
Truth be told, when you have reached the point when cities are huge enough to revolt, you can usually steamroll the entire map, and nasty surprises like gold chevron rebels keep me playing the campaign till the end.

Well, if you can't face the rebels without suffering heavy losses, you can always let the siege go to its term, they will either surrender or try a desperate sally where you'll have a strategic advantage.
The drawback is that your (former) city won't participate in the budget for a long time (don't build epic walls everything to prevent this)

edit
forgot to mention this, if you raze the military buildings and the arena, you'll have peasants army; if you raze military buildings only, you're pretty sure to face gladiators; and if you don't raze any buildings, you can face any kind of army.
now, bear in mind that what I'm saying is not fullproof, just something I saw from experience.