The First Achaemenid Period (525–404 BC) began with the Battle of Pelusium, which saw Egypt conquered by the expansive Achaemenid Empire under Cambyses, and Egypt becomes a satrapy. The Twenty-seventh Dynasty of Egypt consists of the Persian emperors - including Cambyses, Xerxes I, and Darius the Great - who ruled Egypt as Pharaohs till Darius II.
Unfortunately for this dynasty (the 26th), a new power was growing in the Near East – the Achaemenid Empire of Persia. Pharaoh Psamtik III had succeeded his father Ahmose II for only 6 months before he had to face the Persian Empire at Pelusium. The Persians had already taken Babylon and Egypt was no match for them. Psamtik III was defeated and briefly escaped to Memphis, before he was ultimately imprisoned and, later, executed at Susa, the capital of the Persian king Cambyses, who now assumed the formal title of Pharaoh.