Sakaryaformerly Adapazarı ,city, northwestern Turkey, lying in a fertile plain west of the Sakarya River. It is situated along the old military road from Istanbul. The region came under Ottoman control in the early 14th century, and the city acquired its present name at the end of the 18th century. An agricultural and industrial centre, Adapazarı Sakarya is connected by a branch line to the main Anatolian railway system by which its wheat, tobacco, fruits, and vegetables are transported to the Istanbul markets. The city has a large sugar beet processing plant. A stone bridge that was built during the reign of the Roman emperor Justinian is the only surviving ancient monument. Pop. (19852000) 152283,291752.