The fortress Kleiner Feldberg , often referred to in technical literature as Feldberg Fortress or Feldbergkastell , was a Roman military camp whose crew was responsible for security and surveillance tasks at the Upper Germanic Limes . The plant was built on the northern slope of the second highest elevation in the Taunus , the Kleiner Feldberg . This is located in the Hochtaunuskreis below the Hochtaunusstraße . Near the fort lies the source of the Weil . With its north wall the Fortification stands on the border between glassworks and theSchmittener district Niederreifenberg . The altitude of more than 700 meters above sea level makes the Feldbergkastell the highest military camp on the entire Upper German-Raetian Limes.