In my expansion game playing as Rome I got a surprising and pleasant shock. I had taken over both Italia Superior & Italia Inferior and was preparing to prosecute war against Rhaetia and its client state Insubre (Rhaetia declared it) and had lots of citizen hoplites (city defender bonus) as garrisons - two in every city I owned.
I then got the message about building a Campus Martius in order to get early legions from the Senate. Well... I'd already built the Campus Martius much earlier in Rome/Latium though it was available in other places for construction also (thought that was a bit odd but if you'd lost Latium it made sense). The next turn the mission was accomplished and...

BOOM!
All 32 of my citizen hoplites (26 were garrisons) and two armored hoplites became Early Roman Legions!
First thought was. "Nice!"
Second one was, "Oh crap, that's gonna cost a lot in maintenance!"
Luckily my economy is okay and absorbed it.
Persia is kicking butt in the east. I'll see if I can get a screenshot and post it later tonight when I get home from work.
I've gotten the mission to increase loyalty in Latium to 110 three times and failed all three, ain't gonna happen for a while longer LOL.