• 525 BC -- Egypt: End of Twenty-sixth Dynasty[?], start of Twenty-seventh Dynasty[?]
• 521 BC -- Darius I succeeded Gaumata as ruler of Persia
• 520 BC -- Zhou dao wang[?] becomes King of the Zhou Dynasty of China but dies before the end of the year.
• 520 BC -- Cleomenes I[?] succeeds Axanadridas[?] as king of Sparta. (approximate date)

Significant People

• 528 BC -- Death of Cyrus the Great, ruler of ancient Persia
• 527 BC -- Death of Peistratus, Athenian[?] general
• 525 BC -- Birth of Aeschylus, author of Greek tragedies[?]
• March 521 BC -- Death of Cambyses, ruler of ancient Persia (suicide)
• October 521 BC -- Death of Gaumata, ruler of ancient Persia
• 521 BC -- Death of Zhou jing wang[?], King of the Zhou Dynasty of China.
• 520 BC -- Death of Zhou dao wang[?], King of the Zhou Dynasty of China