Players of Caesar III are immersed in a city simulation set in the age of the ancient Roman Empire. Players place buildings on previously empty terrain and construct a city. These buildings come to life, and the city begins to evolve. As the city grows, it encounters various problems which must be overcome. Players have specific objectives to achieve, although many players will not use these, but rather will content themselves in designing their idea of the perfect city.

The game is structured as a career, beginning with a training mission, and then progressing through a series of ever tougher real assignments. Each mission/assignment consists of a province and set objectives. Achieving these objectives will result in promotion and an offer of a tougher assignment, which can be turned down if the player is having too much fun to accept at that time.

The career progression allows us to introduce elements of the game step by step, thereby teaching players how to play without forcing them to play through something called a tutorial. This technique has been extremely well-used in games such as Warcraft.

There will also be a "City Construction Kit" option, where players ignore the career progression, and simply play the full game with no promotion involved.