the population centers of the lahngau developed from places established at fords on the lahn. some of these places go back, according to archaeological finds, to frankish camps of the 6th and 7th centuries that secured crossings of the lahn. the urban centers of the niederlahngau were the later cities of diez (first mentioned as ""theodissa"" in 790) and limburg (first mentioned as ""lintpurc"" in 910). the centers that developed in the oberlahngau were wetzlar (first mentioned as ""weftifa"" in 832), haiger (first mentioned as ""haigrahe"" in 778), and, depending on the course of the border, weilburg (first mentioned as ""wilineburch"" in 906).