539 BCE

28? – Battle of Opis: Troops of the Persian Achaemenid Empire under Cyrus the Great decisively defeat those of the Neo-Babylonian Empire. Fall of Babylon: Achaemenid troops under Gobryas enter Babylon unopposed. Cyrus enters the city, incorporating the Neo-Babylonian Empire into the Achaemenid Empire and turning the latter into the largest in the history of the world up until that point.

In the 530s BC, the 6th century BC.