Trebinje is a city and municipality in Republika Srpska entity, Bosnia and Herzegovina. It is the southernmost city in Bosnia and Herzegovina a…Trebinje is a city and municipality in Republika Srpska entity, Bosnia and Herzegovina. It is the southernmost city in Bosnia and Herzegovina and is situated on the banks of the 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, also known as Perovića Bridge.