Astacus /ˈæstəkəs/ (Greek Ἀστακός Βιθυνίας) is an ancient city in Bithynia; it was also called Olbia /ˈɒlbiə/.
[11] Strabo wrote that some time after Astacus was 'a colony of Megarians and Athenians', it was 'of Doidalsos', whose identity is not specified.
[12] In Historia Augusta is written that at some point Scythians invaded Bithynia and set fire at the city and plundered it cruelly.
[13] King Zipoetes I of Bithynia made two attempts to absorb Astacus into his kingdom: in 315 BC he was defeated by succors sent by Antigonus Monophthalmos.
[4] Nicomedes I, son of Zipoetes, founded a new city to replace Astacus across from its former location, which he named Nicomedia after himself, bringing some of the Astacan cults to the new site.