Year 311 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Brutus and Barbula (or, less frequently, year 443 Ab urbe condita). The denomination 311 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.
In view of the threat by Seleucus to his control of the East, Antigonus decides to make peace with all of his adversaries, except Seleucus, who now holds Babylon. All of the diadochi confirm the existing boundaries and the freedom of the Greek cities. Ptolemy and Lysimachus are confirmed as satraps of Egypt and Thrace, respectively, and Antigonus and Cassander are confirmed as commanders of the army in Asia and Europe. Antigonus, no longer regent but now titled the strategos (officer in charge) of the whole of Asia, rules in Syria from the Hellespont to the Euphrates, including Asia Minor.
The peace agreement between the diadochi is soon violated. On the pretext that garrisons have been placed in some of the free Greek cities by Antigonus, Ptolemy and Cassander renew hostilities against him.