A drydock is a narrow basin or vessel that can be flooded to allow a load to be floated in, then drained to allow that load to come to rest on a dry platform. Drydocks are used for the construction, maintenance, and repair of ships, boats, and other watercraft.
According to the ancient Greek author Athenaeus of Naucratis (V 204c-d), the drydock was invented in Ptolemaic Egypt

Ptolemaic Egypt

Ptolemaic Egypt began when Ptolemy I Soter invaded Egypt and declared himself Pharaoh of Egypt in 305 BC and ended with the death of queen Cleopatra VII of Egypt and the Roman conquest in 30 BC. The Ptolemaic Kingdom was a powerful Hellenistic state, extending from southern Syria in the east, to...

, some time after the death of Ptolemy IV Philopator

Ptolemy IV Philopator

Ptolemy IV Philopator , son of Ptolemy III and Berenice II of Egypt was the fourth Pharaoh of Ptolemaic Egypt...

 (reigned 221-204 BC):
Since Athenaeus recorded the event 400 years later (around 200 AD), there is sufficient reason to believe that drydocks had been known throughout classical antiquity.