The game unfolds in 0 A.D. in exactly the same way as 'Age of Empires II'. That is, you start with a few villagers and a scouting unit, and your goal is to build a great powerful city full of new buildings and strong defences. This will then become your base from where you must expand, build alliances and annihilate your opponents.
To build your city, improve it, and build an army, you need resources. Meat, stone, wood and metal are the main ones that you must always have in plentiful supply in order to keep your villagers working.
In 0 A.D. you can play as nine different civilizations, including the Greeks, Romans, Persians and Britons. Each one has its own buildings, its own advantages, and its own military units. Everything has been customized with great care and attention to make each civilisation as historically accurate as possible.
Although 0 A.D. started out as an 'Age of Empires II: The Age of Kings' clone, it soon evolved into a standalone game with its own graphics engine. And it shows. 0 A.D. is very strong visually, and gets much closer to the third instalment of the 'Age of Empires' franchise.
0 A.D. is an outstanding real time strategy game that is open source and free to play. Furthermore, despite being in the very early stages of development, it already offers a far superior gaming experience to many commercial titles.