Gulf of İzmit (Turkish: İzmit Körfezi), anciently, Sinus Astacenus and Olbianus Sinus (Ancient Greek: Ὀλβιανὸς κόλπος, romanized: Olbianos kolpos), also referred to as Izmit Bay, is a bay at the easternmost edge of the Sea of Marmara, in Kocaeli Province, Turkey.[1] In antiquity it was known first as the Gulf of Astacus and later as the Gulf of Nicomedia.[2]