Random question: what follows an army?

A lot of how the Roman Empire spread its culture was sending the military to new places, defeating anyone who opposed them, and setting up shop.  Everything else came to the army without having to be asked.

Things came at different rates, though.  You didn't exactly have playwrights and poets saying, "Hey, there's a military camp over there.  No buildings yet, just a bunch of soldiers in tents, I should move there to pursue my dreams."  On the other hand the brothels were set up pretty much as fast as the military pitched their tents.  Buildings could come later, soldiers were willing to pay for sex now.

So what I've found myself wondering is what follows the army and at what rate.  Who's there pretty much as soon as the soldiers, who is a bit later, and all the way down to "these people don't show up until it's most definitely become a town or city in its own right."

I've got three posts in the works in an active "I actually want to finish and post this soon" kind of way and I've got a couple more in development, but I'm going to be busy with other things, so they won't be done today.

I've had this question on my mind for a bit, especially in a context where there aren't yet decent trade routes set up, so I figured I'd ask it as a post for today.