Plovdiv (Пловдив) is the second-largest city in Bulgaria after Sofia, with a population of 378,107. blank">General Directorate of Citizens' Registration and Administrative Services: Population Chart as of December 15, 2007 for the City of Plovdiv (Bulgarian). Retrieved on 2007-12-18 . It is the administrative centre of _Plovdiv Province in southern Bulgaria, as well as the largest and most important city of the historical region of Upper (or Northern) Thrace, famous for its ancient and diverse culture and millennial history.