The Late Period includes the last periods during which ancient Egypt functioned as an independent political entity. During these years, Egyptian culture was under pressure from major civilizations of the eastern Mediterranean and the Near East. The socioeconomic system, however, had a vigor, efficiency, and flexibility that ensured the success of the nation during these years of triumph and disaster. Throughout the Late Period, Egypt made a largely successful effort to maintain an effectively centralized state, which, except for the two periods of Persian occupation (Twenty-seventh and Thirty-first dynasties), was based on earlier indigenous models. Late Period Egypt, however, displayed certain destabilizing features, such as the emergence of regionally based power centers. These contributed to the revolts against the Persian occupation but also to the recurrent internal crises of the Twenty-eighth, Twenty-ninth, and Thirtieth dynasties. The Twenty-sixth Dynasty was founded by Psammethichus I, who made Egypt a powerful and united kingdom. This dynasty, which ruled from 664 to 525 B.C., represented the last great age of pharaonic civilization. The dynasty ended when a Persian invasion force under Cambyses, the son of Cyrus the Great, dethroned the last pharaoh. Cambyses established himself as pharaoh and appears to have made some attempts to identify his regime with the Egyptian religious hierarchy. Egypt became a Persian province serving chiefly as a source of revenue for the far-flung Persian (Achaemenid) Empire. From Cambyses to Darius II in the years 525 to 404 B.C., the Persian emperors are counted as the Twentyseventh Dynasty. Periodic Egyptian revolts, usually aided by Greek military forces, were unsuccessful until 404 B.C., when Egypt regained an uneasy independence under the short-lived, native Twenty-eighth, Twenty-ninth, and Thirtieth dynasties. Independence was lost again in 343 B.C., and Persian rule was oppressively reinstated and continued until 335 B.C., in what is sometimes called the Thirty- first Dynasty or second Persian occupation of Egypt.