evidence: Geography of Bosnia and Herzegovina [...] The Sava is the longest river in Bosnia and Herzegovina. However, within Bosnia and Herzegovina, it only runs along the border with Croatia. It then flows into Serbia. Towns like Brčko, Bosanski Šamac, and Bosanska Gradiška lie on the river. Phytogeography [edit]Phytogeographically, Bosnia and Herzegovina belongs to the Boreal Kingdom and is shared between the Illyrian province of the Circumboreal Region and Adriatic province of the Mediterranean Region. According to the WWF, the territory of Bosnia and Herzegovina can be subdivided into three ecoregions: the Pannonian mixed forests, Dinaric Mountains mixed forests and Illyrian deciduous forests.