You have 1 objective: become the supreme leader of Rome by occuping Rome and control at least 50 regions.
At the beginning you can choose 1 of the 3 factions to play: Julii, Bruti or Scipii. Each has the same kind of troops and buildings, but starts on a different place and has different faction members. They all start in Italy, with each an own capital. You will find in Italy another faction: SPQR, or if you don't are an expert in Latin, this stands for "Senatus Populusque Romanus". The senate and the people of Rome. The games currency is denari, which will be used to upgrade city's,train armies, or bribe enemy cities or armies.
During the game, you will notice that you will be given missions from the senate, like capture a city or get trade rights. Completing one of those missions will give you a reward, like: 5000 denari or games will be thrown at the senate's expenses. On top of that you will get a certain amount of respect, which will give your own faction members more change to get elected to the senatorial offices, which will give them better traits, which improves their attributes: Command, management and influence. If you don't complete a mission, the opposite can happen.
The things I liked the most are when your empire is getting bigger and more advanced,you will get stronger units. And when you defeat a faction you can be them when you start a new game. I can play this game for hours, and still it wont get boring.