Zwinger, Battery tower in Goslar, Germany

The Zwinger is a circular battery tower built in 1517 on the Thomaswall in Goslar. Its walls are 6.5 metres thick at the base, it measures 26 metres in diameter and stands 20 metres high. The original conical roof was removed in 1857. Today the ground floor houses a restaurant, the middle floor three holiday apartments and the top floor a small museum of medieval weapons, armour and torture implements.

This fortification was built in 1517 on Thomaswall to protect the imperial city of Goslar from potential attacks originating from the Rammelsberg hill position. The construction reflected the city's defensive strategy at that time.

Two sandstone tablets set just below the corbelling carry the coats of arms of the German Empire and of Goslar, with the inscription "Anno dm M D X V II" recording the year 1517. The tower has been in private hands since 1 August 1936; today its floors hold a restaurant, three holiday apartments and a small museum of medieval weapons, armour and torture implements.

The tower stands on the Thomaswall in the south of Goslar, on the side overlooked by the Rammelsberg. The ground floor holds a restaurant, the middle floor three holiday apartments and the top floor a small museum of medieval weapons, armour and torture implements; the apartments are private, so visitors see the museum and restaurant.

The builders mixed the mortar with horsehair, curds, goat milk, and ox blood to achieve proper hardening of the structure. This unusual recipe shows the resourceful building methods used in that era.