What is included in the Rome: Total War - Alexander expansion pack?

The Rome: Total War - Alexander expansion pack contains the following additional features:

• An entirely new campaign.
• Over 50 new units including the Persian Immortal Infantry, Indian War Elephants and the renowned Macedonian Companion Cavalry.
• Four new playable factions: the armies of Macedon, Persia, India and the barbarian Dahae.
• Six historical battles based on Alexander’s greatest victories.