The larger pack, titled "Mongols Civilization and Scenario Pack," includes the Mongol civ and the infamous Genghis Kahn as playable entities, bringing their own special horsemen. The included scenario will test your ability to recreate the Mongols' long and hard conquest of Asia. This pack will be free, as a "gift to the legions of Civ fanatics." Yay!
The other download, "Babylonian Civilization Pack," doesn't include any scenarios or special maps, but allows players to take control of the Babylonian Bowmen under the care of King Nebuchadnezzar II. Since they were previously exclusive to the Civilization V Digital Deluxe Version, this civ will run you $4.99. But at least then you won't feel left out!
With these two packs coming out soon, it's difficult to tell whether Firaxis plans on supporting their PC hit with paid DLC or free add-ons in the future. This step also may be a way of inspiring the active mod community into building their own scenarios and add-ons, since Civilization V's in-game content browser makes it easy to view and install community works for free. I certainly wouldn't mind seeing more historical scenarios recreated on Civ's grand scale.
Both DLC packs will be up for download on October 25!