Berthold V, Duke of Zähringen founded the city of Bern. For strategic reasons it was necessary to have a strong fortification on the peninsula formed by the Aare river, and the Duke accordingly entrusted one of his noblemen with the task of building a city there.At the extreme end of the peninsula already stood a mighty castle, built probably in the II century as a free imperial castle. In the course of the 12th century, a small settlement had sprung up around the so-called Nydegg CastIe. Cuno of Bubenberg, who was responsible for the execution for the Duke's orders, had the oak forest, covering the peninsula, cut down and the wood of these trees was used to build the first houses. That was in the year 1191 when Bern was part of Upper Burgundy, ruled by the Dukes of Zähringen, who had been appointed to this position by the Emperor Lothair IIl. Cuno of Bubenberg built a first city wall in the center of which rose the great Zytglogge (Clock Tower) functioning at the same time as main gate giving access to the countryside beyond. In front of the city wall was a natural hollow in the ground which served as moat.