31 BC

Year 31 BC was either a common year starting on Tuesday, Wednesday or Thursday or a leap year starting on Tuesday or Wednesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Antonius and Octavianus.

Events
 Gaius Julius Caesar Octavian becomes Roman Consul for the third time. His partner is Marcus Valerius Messalla Corvinus, replacing Mark Antony.
 Octavian establishes a bridgehead at the Gulf of Ambracia
 Marcus Vipsanius Agrippa sailed with 300 war galleys to the western Peloponnese. He occupied the Gulf of Corinth to cut off Antony's line of communication.
 Antony sets up camp at the promontory of Actium.
 Agrippa stormed Leucas. He took the garrison at Patrae.
 The Egyptian fleet retreats to Taenarus.
 Octavian takes court at Samos
 In the Judean Desert Herod the Great completes the fortress Masada.
 The Hellenistic period in art ends (or AD 14 by some scholars)