0 A.D. (pronounced “zero-ey-dee”) is a free, open-source, historical Real Time Strategy (RTS) game currently under development by Wildfire Games, a global group of volunteer game developers. As the leader of an ancient civilization, you must gather the resources you need to raise a military force and dominate your enemies.
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We intend to portray some of the major civilizations over the millennium of 500 B.C. to 500 A.D. (Hence the midpoint, zero.) That is an ambitious prospect, so in the first edition of 0 A.D. we focus on the last five centuries B.C. Perhaps in future expansion packs, more civilizations will be added, along with additional gameplay features.

We put a strong emphasis on historical accuracy while developing 0 A.D. We plan all our units and all our buildings based on reconstructions of how the units and the buildings might have looked like in the ancient world. We even name them in the original languages, such as Greek and Latin. But it’s worth remembering that any game should be fun to play, so, in many cases, we preferred playability over historical accuracy.

Source: 0 A.D. | A free, open-source game of ancient warfare