285 BCE

Egypt's Ptolemy I Soter abdicates. He is succeeded by his youngest son by his wife Berenice, Ptolemy II Philadelphus, who has been co-regent for three years. Demetrius Poliorcetes is deserted by his troops and surrenders to Seleucus at Cilicia, where Seleucus keeps him a prisoner. A 110 metre tall lighthouse on the island of Pharos in Alexandria's harbour is completed and serves as a landmark for ships in the eastern Mediterranean. Built by Sostratus of Cnidus for Ptolemy II of Egypt, it is one of the seven wonders of the ancient world. It is a technological triumph and is the archetype of all lighthouses since. A broad spiral ramp leads to the top, where a fire burns at night.

Geopolitics & Diplomacy

June 26 – Egypt's Ptolemy I Soter abdicates. He is succeeded by his youngest son by his wife Berenice, Ptolemy II Philadelphus, who has been co-regent for three years.source

Conflict & Security

Demetrius Poliorcetes is deserted by his troops and surrenders to Seleucus at Cilicia, where Seleucus keeps him a prisoner.source

Science & Discovery

A 110 metre tall lighthouse on the island of Pharos in Alexandria's harbour is completed and serves as a landmark for ships in the eastern Mediterranean. Built by Sostratus of Cnidus for Ptolemy II of Egypt, it is one of the seven wonders of the ancient world. It is a technological triumph and is the archetype of all lighthouses since. A broad spiral ramp leads to the top, where a fire burns at night.source

Deaths

Theophrastus, Greek philosopher, a native of Eressos in Lesbos, the successor of Aristotle in the Peripatetic school (b. c. 370 BC). 288 B.C. is also given as a potential date of death.source
Dicaearchus, Greek philosopher, cartographer, geographer, mathematician and author (b. c. 350 BC)source