Slavs settled Balkans and all of the current Banja Luka are in the sixth and seventh centuries, and they built several fortresses in the valley of the river Vrbas. There are not many written records from that time. The earliest Slavic settlement is also called "Vrbas," and it was first mentioned in 1320. The name of the town Banja Luka first appears in writing in 1494, in a work by Croatian-Hungarian King Vladislav. The name comes from "banjaluk" that is the Turkish-Bosnian slang for "spaing." This is because of the natural hot water suitable for baths that still exist in today's oldest settlement, Gornji Šeher/Upper Seher. The city came under Ottoman rule in 1537.