Cleitus fled to Macedon and joined Polyperchon, the new Regent of the Empire, who decided to march his army south to force the Greek cities to side with him against Cassander and Antigonus. Cassander, reinforced with troops and a fleet by Antigonus, sailed to Athens and thwarted Polyperchon's efforts to take the city. From Athens Polyperchon marched on Megalopolis which had sided with Cassander and besieged the city. The siege failed and he had to retreat losing a lot of prestige and most of the Greek cities. Eventually Polyperchon retreated to Epirus with the infant King Alexander IV. There he joined forces with Alexander's mother Olympias and was able to re-invade Macedon. King Philip Arrhidaeus, Alexander's half-brother, having defected to Cassander's side at the prompting of his wife, Eurydice, was forced to flee, only to be captured in Amphipolis, resulting in the execution of himself and the forced suicide of his wife, both purportedly at the instigation of Olympias. Cassander rallied once more, and seized Macedon. Olympias was murdered, and Cassander gained control of the infant King and his mother. Eventually Cassander became the dominant power in the European part of the Empire, ruling over Macedon and large parts of Greece.