Age of Empires Online's march to retail will conclude this fall, the game's official Twitter announced, with a Microsoft rep informing us a specific launch date is expected to be revealed May 31.

After launch, the freemium title will have "a parade of Premium Content" at under $20. The additions include two more civs to keep the Greeks and Egyptians company by the end of 2011, along with a "Premium 'Pro' Civilization" pack that will advance players immediately to level 20 for "expert play."

Check out our Age of Empires Online preview for what to expect from the initial experience.