the exact demarcation of the boundary between oberlahngau and niederlahngau has not survived. according to some historians, the approximate boundary is presumed to have been the watershed between the solmsbach and the weil river, east of weilburg. christian spielmann writes in 1894, “weilburg lay in the niederlahngau. it extended from about the nister to the pfahlgraben and from the gelbach and aar westward to the ulmbach and eastward to weil. other historians suggest the border was west of weilburg. hellmuth gensicke suggested the watershed between the kerkerbach and elbbach as a possible boundary. the following discussion is based on the interpretation of gensicke assuming a border west weilburg.