The Kale Fortress (Macedonian Скопско кале, Albanian Kalaja e Shkupit) is located on a hill west of the old town and on the north side of the Vardar. The first traces of human settlement at the castle date back to the 4th millennium BC. Under the Bulgarian tsar Samuil (10th century AD) a fortified settlement stood on the hill for the first time. In 1391 the city and the surrounding region were conquered by the Ottomans. The war destroyed large parts of the city, including the fortress. After that, the castle served as a barracks for the Ottoman troops. The fortress and Skopje then lost their economic importance in the region. Around 1700 the castle was renewed again. Today's outer wall, towers and gates also date from this period. The east gate was the most important; it led straight into the bazaar. Even in the 20th century the fortress served as a barracks for the troops of the Kingdom of Yugoslavia; ten large military buildings, headquarters and barracks were built. In 1951 the armies withdrew and the Archaeological and Historical Museum took over the management. During the severe earthquake of 1963, most of these modern buildings were destroyed. Since then, numerous archaeological works have been carried out on the fortress.