In case your game is not patched, you can patch it up for free by downloading the 1.6 patch* from Is it easy to install a mod? We recommend the Steam version (around $10 or less) as the old disk versions, as of September 2015, require workarounds to work with the Windows operating system (see the "Support" link above for more information). Normally you can find the game and the extension packaged together in a bundle called Rome: Total War Gold Edition (though there are other editions). The Dominion of Men is created for a game called Rome: Total War developed by the Creative Assembly and requires that you also have the expansion, Barbarian Invasion, patched to 1.6 (the final patch). This, of course, will not only allow you to play the mod but also the original game and a plethora of other quality mods - all for free! In fact, we even recommend some of the best mods for you (see the "More Mods…" link above). You will need to purchase the game engine.
The distribution of mods to the public extends the lifetime of a game engine, and so game development companies usually allow such distribution with the caveat that mods cannot be commercial in nature. A mod may enhance gameplay, or it may entirely convert the setting into one quite different from the original game. A mod is a modification of a commercial game engine that creates a new playing experience for the player.