The Hellenistic period begins, in Mesopotamia, with the conquest of Babylon by Alexander the Great in 331 BCE. The reign of Alexander and the wars between the Diadochi, his successors, is now commonly known as the Macedonian period. It precedes the Seleucid era. According to the Macedonian and Babylonian calendars, it official begins in 312-311, but in reality it dates from the recapture of Babylon by Seleucus in 305. After proclaiming himself king, Seleucus dated the start of his reign to 312-311, when he first returned to Babylonia. The Seleucid period in Babylonia ended with the conquest of the region by the king of the Parthian Empire, Mithridates I (165-131) in 141 BCE.