Imperium Romanum is a city-builder set in the ancient Roman Empire. If you're thinking, "Hey that sounds just like the old Caesar series" then you're not far off. Much like the old Sierra series, Imperium Romanum places you in a series of towns and settlements and asks you to build housing, establish farming and resource production, and set up industries. You'll also build defenses and armies to protect yourself from barbarian hordes and conquer nearby villages.
I think Imperium Romanum takes a slightly more casual and less complex approach to the genre. First, at least in the missions I played, each level seemed to be completely contained and it didn't seem as though your city carried over throughout multiple stages of the campaign. Rather, each mission starts in a different settlement and gives you goals to accomplish there and then you move on to the next. There is a sandbox gameplay option so if you want to build a super-city, you can do that, but the campaign missions don't seem to be cumulative.
Combat is rather simplistic and basically your troops are limited to a couple of formations, neither of which can actually be changed on the fly once battle has begun.
One thing I did notice here is that unlike a lot of the "historical" city management titles, the game doesn't skirt around the issue that slavery was a common practice. Slaves will do all the building and hauling here, and they get separate "housing" and will not be able to fill the "free" jobs that your settlers will take. If you overwork your slaves (i.e. don't build enough slave shelters) then they are likely to revolt until you get their workload under control.
The graphics are pretty detailed and there is a nice variety of industries and buildings you can introduce in your town.
Overall, it's a nice little city builder for the history buffs, and it offers a more forgiving approach to planning than some of the other similar games I've played. (read this as: I never had to break out a spreadsheet to lay out perfect housing and industrial blocks in Imperium Romanum in order to beat a level. Then again, I might have been an overly compulsive Caesar player. ymmv)