Bosnia (, ) is the northern region of Bosnia and Herzegovina, encompassing roughly 81% of the country; the other region, the southern part, is Herzegovina. The two regions have formed a geopolitical entity since medieval times, and the name "Bosnia" commonly occurs in historical and geopolitical senses as generally referring to both regions (Bosnia and Herzegovina). The official use of the combined name started only in the late period of Ottoman rule. Geography Bosnia lies mainly in the Dinaric Alps, ranging to the southern borders of the Pannonian plain, with the rivers Sava and Drina marking its northern and eastern borders. The area of Bosnia comprises approximately 39,021 km2, and makes up about 80% of the territory of the present-day state of Bosnia and Herzegovina. There are no true borders between the region of Bosnia and the region of Herzegovina. Unofficially, Herzegovina is south of the mountain Ivan planina. According to another unofficial definition, Herzegovina encompasses the watersheds of the Neretva and Trebišnjica rivers. History The Central part of Bosnia was inhabited by Neolithic farmers that belonged to the Kakanj culture, and later replaced by another neolithic culture called the Butmir culture. The first Indo-Europeans are thought to be members of eneolithic Vučedol culture. In the Bronze Age the area is thought to have been inhabited by Iron Age Central Bosnian cultural group and Glasinac culture. Later on the Illyrian tribe of the Daesitiates would become dominant in these area. The historical records of the region are scarce until its first recorded standalone (domestic) ruler and viceroy of Bosnian state, Ban Borić, was appointed in 1154. De Administrando Imperio describes a small Serbian župa of Bosona () that was located around the river Bosna in the modern-day fields of Sarajevo and of Visoko. Under its first known by name ruler, Stephen, Duke of Bosnia, in the 1080s, the region spanned the upper course of the rivers Bosna, the Vrbas and the Neretva. At the end of the 14th century, under Tvrtko I of Bosnia, the Bosnian kingdom included most of the territory of today's Bosnia and of what would later become known as Herzegovina. The kingdom lost its independence to the Ottoman Empire in 1463. The region of Bosnia's westernmost city at the time of the conquest was Jajce. The Ottoman Empire initially expanded into Bosnia and Herzegovina through a territory called the Bosansko Krajište. It was transformed into the