In June/July 1389, the Archbishop started construction of the “Meerturm” or Marsh Tower to improve the defensive strength of the castle and to secure the “Meertor” or Marsh Gate. The “Meerturm” is a type a tower, which was typical of the last decade of the 14th Century. The other gate towers only permit access to the city via a passage at ground level. The Meertor was built onto the fortified tower. Compared with the other city gates, the Meertor was quite small, since the area in front of the gate and the Meerturm was very marshy and an attack from this direction was deemed unlikely. Far more impressive was the Meerturm that was built to protect the entrance to the city. In the Lower Rhine dialect, Meer means moor or marsh. Thus, the marshy area in front of the Meerturm gave the tower its name. Later on, however, the meaning was forgotten and the tower was even known as the Martpoort or the Martyr’s tower. Thanks to its thick walls, it survived the attempts at demolition at the beginning of the 19th Century. Due to its uneven masonry, the tower, classified as an historical monument, still shows the foundations and height of the old city wall on the south facing side. Something else can be seen there. A dark basalt mark in the road surface denotes where once stood the northern wall of the Meertor. Today, the Meerturm and the Meertor form part of the Siegfried Museum. The exhibition halls of museum.de are accommodated in the Meerturm.