In the first half of the 15th century, the tower was raised to 6 stories. The lions, an embodiment of defensive vigilance in Romanesque art, are executed in a characteristically stylised manner. One lion grasps a ram in its paws, sometimes interpreted as a symbol of the power of the Church, while the second grasp a dragon or other fabulous animal, symbolizing secular power.

On the Rhine side, the arch is embellished with two Romanesque carvings of lions in sandstone, atop ornamental capitals over fluted cornerstones. The round-arched late Romanesque gateway at the base of the tower dates to the first half of the 13th century, probably around 1240. Late Romanesque carving of a lion on the Iron Gate ( c. The Iron Tower was built in this phase of construction, as one of a total of 34 gate towers and watchtowers. However, Mainz was an important political and strategic ally in the Hohenstaufens' struggle for supremacy in the German Empire against the Welfs, and so in circa 1190–1200 the city was granted permission to rebuild the defences. The city walls and towers were razed (although it is possible that on the inland side the destruction was only partial). There was a longstanding dispute between the citizens of Mainz and their archbishop, Arnold of Selenhofen (and also with the Holy Roman Emperor Frederick Barbarossa) after the archbishop was murdered, the emperor imposed an imperial ban on the city. However, in 1160 the continuity of the city's defenses was drastically interrupted. After the Romans withdrew, it was improved at various times, particularly in the Merovingian and Carolingian periods, becoming what archaeologists studying the city have called the 'Roman-Carolingian' wall. Not long after 350, in the course of the abandonment of the Roman camp, this wall was lowered and rubble ( spolia) from earlier construction used to enlarge and strengthen it. The first wall was built shortly before the destruction of the limes in 259/260 CE. Since late Roman times, the city of Mainz (then Mogontiacum) was defended by a wall with watchtowers and city gates. Historical background: the defenses of Mainz Today it houses various organizations and art projects and is used for art exhibitions. It was badly damaged in World War II and reconstructed in the 1960s.

The Iron Tower served as a watchtower and gate to the city, and later as a gaol. Its name derives from the Iron Market ( Eisenmarkt), which was held in the immediate vicinity until the 19th century. The Iron Tower ( German: Eisenturm) is a mediaeval tower dating to the early 13th century, and modified in the 15th century, which with the Wood Tower and the Alexander Tower is one of three remaining towers from the city walls of Mainz, Germany.

The Iron Tower by Dennis L. McKiernan