The Rhodope Mts. separate Greek from Bulgarian Thrace, and the Maritsa River (called the Évros in Greece) separates Greek from Turkish Thrace. The chief cities are İstanbul, Edirne (formerly Adrianople), and Gallipoli (all in Turkey); İstanbul (Constantinople) is generally considered a separate entity. With the exception of the mountainous Bulgarian section, Thrace is mainly agricultural, producing tobacco, corn, rice, wheat, silk, cotton, olive oil, and fruit. Natural gas has been discovered in the region.