Near the Upper Gate, west of the surrounding wall, which is 1,138 metres long, is the Knoller- or Specht Tower. Gustav Horn, a Swedish general, had the city bombarded from Untergriesbach. The crenellated Knoller Tower was not badly damaged. Perhaps a part of the crenellation slid down in 1775 during the heavy earthquake in Lisbon, which also affected Aichach.