Rostov-on-Don[a] is a port city and the administrative centre of Rostov Oblast and the Southern Federal District of Russia. It lies in the southeastern part of the East European Plain on the Don River, 32 kilometers (20 mi) from the Sea of Azov, directly north of the North Caucasus. The southwestern suburbs of the city lie above the Don river delta. Rostov-on-Don has a population of over one million people and is an important cultural, educational, economic and logistical centre of Southern Russia. From ancient times, the area around the mouth of the Don River has held cultural and commercial importance. Ancient indigenous inhabitants included the Scythian and Sarmatian tribes. It was the site of Tanais, an ancient Greek colony, Fort Tana under the Genoese, and Fort Azak in the time of the Ottoman Empire.