Unlockable units
Here are all of the unlockable units. You use empire points that you earn in matches to purchase them. To purchase them, just go to "bonus items" in the main menu.

Dark Ram - 150 empire points
Dopple- handers - 100 empire points
Genoese Crossbowmen - 100 empire points
Knights of the Round Table - 200 empire points
Mons Meg - 150 empire points
Swiss Pikemen - 100 empire points
War Wolf - 150 empire points
Welsh Bowmen - 100 empire points

Bonus maps
Select the "Bonus Items" option at the main menu to buy the indicated map in Empire Map mode for the corresponding amount of Empire points.

Agincourt: 250 Empire points
Archipelago Large: 200 Empire points
Asia Major: 300 Empire points
Bridges Large: 100 Empire points
Castles: 150 Empire points
France: 100 Empire points
Hannibal's Crossing: 250 Empire points
Hastings: 250 Empire points
Khyber Pass: 250 Empire points
King Of The Mountain: 300 Empire points
Outremer: 150 Empire points
Skirmish - Desert: 250 Empire points
Skirmish - Plains: 250 Empire points
Swamplands: 150 Empire points
Valley: 100 Empire points

Black Market
Complete all campaigns with all characters to unlock the Black Market icon at the main menu. This will allow you to buy previously unreleased characters, maps, campaigns, and movie clips.