On Zuckerberg there are the remains of a defensive tower called “Bolander“. At this extreme south-west corner of the Kaiserpfalz it was the strongest of the original four fortified towers. They were built to protect the southern and western flanks of the Pfalz and its entrance, the “Rheingässer Tor“ (Rhine Alley gate). An early depiction of the Saal area in the “Cosmographia – Beschreybung aller Lender“ (cosmography – the description of all countries) by Sebastian Münster (1489-1552) shows the tower was topped by embrasures and battlements. The name Bolander can be traced back to the dynasty of ministeriales of the lords of Bolander, who owned the imperial bailiwick in Ingelheim and a customs station in the Pfalz district until the 13th century.
Only 4 metres remain of the original multi-storey tower. Inside the tower (not accessible to the public) holes for beams indicate that the building material inside was wood, of which stairs and floors were made. The tower‘s diameter is 2.8 metres and the wall is 3.2 metres thick. The defensive tower is an element in the fortification of the Pfalz district, the construction of which was presumably begun in 1160. After the pledging of the Kaiserpfalz in 1375, the fortifications served as a town wall until their destruction during the Orleans war in the area of the Kurpfalz (1688-1697). Texts, drawings and remains of buildings confirm that the fortifications were often repaired and maintained and further fortification was added to update the building. Further remnants of these fortifications can be seen on Zuckerberg, at the Heidesheimer Tor and in the upper Karolingerstraße.