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 Dominicalendar era became the prevalent method in Europe for naming years.
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.
Since 480 BC, an aristocratic Council of Elders has effectively ruled Carthage. The titular king of Carthage, Bomilcar, attempts a coup to restore the monarchy to full power. His attempt fails, which leads to Carthage becoming in name as well as in fact a republic.
Leaving his brother Antander to continue the defence of Syracuse, Agathocles lands in North Africa with the aim of distracting the Carthaginians from their siege of Syracuse. Agathocles concludes a treaty with Ophellas, ruler of Cyrenaica. He then takes advantage of the civil unrest in Carthage and nearly succeeds in conquering the city.
Soon after the State of Qin has conquered the State of Shu (in modern-day Sichuan province), they employ the Shu engineer Bi Ling to create the Guanxian irrigation system, which will eventually provide for over five million people in an area of 40 to 50 square miles (130 km2), still in use today.