During the game you may unlock Achievements: unique rewards for performing a specific task. Some Achievements are easy to gain, like winning the game when playing as Washington.

Other Achievements will require multiple play-throughs, planning, and effort to unlock.

You can view all available Achievements in the game from Civ V’s Steam 
Game Page.

If you’re playing offline when you fulfill the requirements for an Achievement, the game will store this information and unlock the Achievement for you the next time you log into Steam.

Check back often on Steam for more Achievements – new ones will become available with some DLC packs.