On the north side of Nuremberg's old city stand the powerful buildings of the castle, which is one of the most important fortresses of the Middle Ages. The cliffs tower over the old city, on which the entire collection of castle buildings was constructed during three different phases, Burggrafenburg (castle of the governor of the fortress), Kaiserburg (emperor's castle), and reichsstädtischer Teil (part belonging to the Imperial City). In the center picture, one sees the Fünfeckturm (five-cornered tower), which is the oldest building in the city and belongs to the Burggrafenburg. In the picture, it stands in front of the Kaiserstallung (emperor's stables), which the city operations manager, Hans Behaim, built in the third phase, in 1494-95. This grain storage building served for keeping the horses, when the emperor visited Nuremberg and the Reichstag (imperial diet) met. As a fortress, the Kaiserburg was built in the 12th century under the rule of Konrad III. and later Friedrich I. Barbarossa (with the red beard). In the upper picture, one sees the powerful Sinwellturm (round tower), which originates from this period and whose middle-high-German name, sinwell, means ”round.” The Kaiserburg and particularly the Sinwellturm mark the silhouette of the old city, and metaphorically the Kaiserburg represents the long history of Nuremberg.