Bithynia (/bɨˈθɪniə/; Greek Βιθυνία Bithynia) was an ancient region, kingdom and Roman province in the northwest of Asia Minor, adjoining the Propontis, the Thracian Bosporus and the Euxine Sea.It bordered on Mysia to the south-west, Paphlagonia to the north-east along the Pontic coast, and Phrygia to the south-east towards the interior of Asia Minor.Bithynia was an independent kingdom from 4th century BC.