It is joined by four main tributaries, the Drina, Bosna, Vrbas and Una.
Near Doboj, on the Bosna, there is a state sugar-refinery, for which beetroot is largely grown in the vicinity.
The other, a narrowgauge line, crosses the Save at Bosna Brod, and follows the Bosna to Serajevo, throwing out branches eastward beyond Dolnja Tuzla, and westward to Jajce and Bugojno.
Small steamers ply on the Drina, Save and Una, but the Bosna, though broad from its very source, is, like the Vrbas, too full of shallows to be utilized; while the Narenta only begins to be navigable when it enters Dalmatia.
The later middle ages are represented by several monasteries, and many castles, such as those of Dervent, Doboj, Maglaj, Zepee and Vranduk, on the Bosna; Bihac, on Owing to the scarcity of authoritative documents, it is impossible to describe in detail the events of the next three centuries.