Bithynia (; Greek  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. Its capital Nicomedia was rebuilt on the site of ancient Astacus in 264 BC by Nicomedes I of Bithynia. Bithynia fell to the Roman Republic in 74 BC, and became united with the Pontus region as the province of Bithynia et Pontus, in the 7th century incorporated into the Byzantine Opsikion theme. It became a border region to the Seljuk Empire in the 13th century, and was eventually conquered by the Ottoman Turks in the 1330s.