Trebinje (Serbian Cyrillic: Требиње) is a city located in Republika Srpska, an entity of Bosnia and Herzegovina. It is the southernmost city in Bosnia and Herzegovina situated on the banks of Trebišnjica river in the region of East Herzegovina. As of 2013, it has a population of 31,433 inhabitants. The city's old town quarter dates to the 18th-century Ottoman period, and includes the Arslanagić Bridge. The city lies in the Trebišnjica river valley, at the foot of Leotar, in southeastern Herzegovina, some 30 km (19 mi) by road from Dubrovnik, Croatia, on the Adriatic coast. There are several mills along the river, as well as several bridges, including three in the city of Trebinje itself, as well as a historic Ottoman Arslanagić Bridge nearby. The river is heavily exploited for hydro-electric energy. After it passes through the Popovo Polje area southwest of the city, the river — which always floods in the winter — naturally runs underground to the Adriatic, near Dubrovnik. Trebinje is known as "the city of the sun and platan trees", and it is said to be one of the most beautiful cities in Bosnia and Herzegovina. The city is economic and cultural centre of the region of Eastern Herzegovina.