a former country in southwestern Asia, now called Iran. The ancient kingdom of Persia became the domain of the Achaemenid dynasty in the 6th century bc . Under Cyrus the Great, Persia became the center of a powerful empire that included western Asia, Egypt, and parts of eastern Europe; it was eventually overthrown by Alexander the Great in 330 bc . The country was conquered by Muslim Arabs between ad 633 and 651. It was renamed Iran in 1935.