The conflict between the Habsburg emperor Frederick III and his younger brother Archduke Albert VI of Austria started an unstable period in the region. In 1446, many homes in the town were burned during the invasion of the Hungarian regent John Hunyadi. During this time, the castle was occupied by various rival forces, including mercenaries of King Matthias Corvinus from 1477 until about 1490, when Frederick's son King Maximilian I re-established Habsburg control over the area. This turbulent period interrupted the construction of the tower house ("Wehrturm"), the town's landmark with a height of , which started in 1450 and was finished about 1521. The tower and other fortifications permitted a successful defense of the city against the Ottoman troops during the 1529 Siege of Vienna, while the surrounding area was devastated.