Year 285 BC was a year of the pre-Julian Roman calendar.
|Millennium:||1st millennium BC|
|Centuries:||4th century BC – 3rd century BC – 2nd century BC|
|Decades:||310s BC 300s BC 290s BC – 280s BC – 270s BC 260s BC 250s BC|
|Years:||288 BC 287 BC 286 BC – 285 BC – 284 BC 283 BC 282 BC|
- June 26 – Egypt's Ptolemy I Soter quits ruling. He is succeeded by his youngest son by his wife Berenice, Ptolemy II Philadelphus. He was co-regent for three years.
- A 110 metre tall lighthouse on the island of Pharos in Alexandria's harbour is completed. It is 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.
- Demetrius Poliorcetes is left by his troops and surrenders to Seleucus at Cilicia, where Seleucus keeps him a prisoner.