Bosnia, in the Early Middle Ages to early High Middle Ages, was a territorially and politically defined entity, governed at first by knez and then by a ruler with the ban title, possibly from at least 838 AD. Situated, broadly, around upper and middle course of the Bosna river, between valleys of the Drina river on the east and the Vrbas river on the west, which comprise a wider area of central and eastern modern-day Bosnia and Herzegovina. Wikipedia