Persia refers to an ancient Middle-Eastern kingdom ruled by the inhabitants, known as the Persians which is primarily based on Achaemenid Empire located roughly in present day Iran. The civilization reached its peak under Persian king Xerxes, but slowly fell apart following the conquest of Alexander the Great which occurred just after the Persian naval defeat at Salamis in an attempt to conquer the Greek city states.
The Persians are a playable civilization in Age of Empires and are strictly an offensive civilization which illustrates their rapid expansion of their empire under Cyrus the Great. They can train a variety of elite units and have the best Cavalry units in the game but have poor archery units. Although the Persians have a fast economy near the beginning of the game, their economic might decreases once the game progresses.