When did belshazzar rule?

Answer 1

Belshazzar ruled from roughly 549-539 B.C. as the crown prince under the Babylonian emperor Nabonidus. The actual start of his rule is unknown the earliest mention of it exists on a tablet that was written during the seventh year of Nabonidus' reign. We know his rule ended in 539 B.C. because of the Babylonian Chronicles which state that on October 13, 539 B.C. Gubaru (also known as Darius the Mede) took the city and killed Belshazzar. So the most "confirmable" dates are 549-539 B.C. though his reign may have begun up to seven years earlier when the reign of Nabonidus his father became king.