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Year 309 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Dictatorship of Cursor (or, less frequently, year 445 Ab urbe condita). The denomination 309 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
Events
By place
Asia Minor
- Ptolemy I Soter personally commands a fleet that takes the coastal regions of Lycia and Caria from Antigonus I Monophthalmus, capturing the cities of Phaselis, Xanthos, Kaunos, Iasos and Myndus.
Thrace
- Lysimachus, the Macedonian ruler of Thrace and one of diadochi, founds the city of Lysimachia on the north-western extremity of the Thracian Chersonese (the modern Gallipoli peninsula) to serve as his capital.
Greece
- Cassander, who has held Roxana, widow of Alexander the Great, in prison for a number of years, has her put to death along with her young son Alexander, the nominal King Alexander IV of Macedon.
- Antigonus attempts to renew his alliance with the Macedonian general and former regent Polyperchon, who still controls part of the Peloponnesus. He sends Heracles, the illegitimate son of Alexander the Great, to Polyperchon to be treated as a pretender to the throne of Macedonia.
- Polyperchon manages to form an army consisting of 20,000 infantry and 1,000 cavalry and challenges Cassander's army. Instead of fighting, Cassander starts negotiations with Polyperchon. By offering to make him a general of his own army and placing him as governor of Peloponnesus, he convinces Polyperchon to change allegiance to him instead of Heracles. As a result, Polyperchon murders Heracles and his mother Barsine.
- Areus I succeeds his grandfather Cleomenes II as king of Sparta.