The fort, probably founded in the late 4th century AD, was part of the rear fortification line of the Danube-Iller-Rhine Limes, which was built to protect the long-distance transport connections of the imperial border, which was returned to the Rhine-Danube line under Diocletian and Constantine I had been.
The name "ad Fines" (on the border) does not refer to the imperial border, but to the border between the provinces of Maxima Sequanorum (Gaul) in the west and Rhaetia in the east. Shortly before 300 AD. A mighty fortress was built at this point, the ruins of which can still be seen today in the area of the so-called "Städtli". The north and parts of the west wall are quite well preserved (inside the school complex, opened by the school warden, small exhibition). After 400 AD The fort was abandoned, but the ruins were always visible.
The Bartholomew Church inside the fort is one of the oldest churches in Thurgau and indicates the continued existence of the settlement in the Roman ruins even during the early Middle Ages.