Imperium Romanum is a city building simulation set between 500 BC and 100 AD - in other words: the time of the Roman Empire. It focuses mostly on the economical aspect of the cities and combat has little bearing on the gameplay. As usual the player is in the position of the city planner and constructs all the different buildings needed for functional educational cycles and for satisfying the population, e.g. resource buildings, processing industries, schools, taverns, military and prestige constructions. Most importantly is a logical structure and short production paths.

The game offers no free building mode but only (including the campaign) unrelated missions where the player needs to fulfill certain requirements. The catch: The player decides himself when the game gives him these quests which are concealed in cards. So if the player wants he could build up the city a few hours and then reveal the first card with the first mission or reveal three of them at the same time. There are also optional missions which reward certain bonuses.