The Haller, locally known as Der Haller, lies in the town of Monschau, in the North Rhine-Westphalia region in Germany.
The town of Monschau, situated in a small valley of the Rur river, has two fortifications; Monschau Castle and the Haller. The first is a proper castle, mainly built in the 14th century, on one side of the valley. The latter probably a tower house from the 13th century on the other side of the valley.
At first it was thought that the Haller was a watch tower, belonging to the castle. At present it is believed to be older than the castle and not connected to it. Probably this was the first fortification in Monschau before its owners decided to build a new castle on the other side of the valley.
In 1534, when Monschau Castle was besieged by the troops of Charles V, the Holy Roman Emperor, the Haller still had a roof. In 1570-71 building materials were taken from the Haller to repair the castle. From the second half of the 17th century the Haller was used as a powder magazine and guardhouse and was equipped with a temporary roof again. Somewhere during the 18th century it lost its roof and function and fell to ruin.
In 1971 the Haller was wrapped, together with the castle, for an environmental art project by the artist Christo.
The exterior of the Haller can freely be visited. Its interior is unaccessible. A small and architectural rather uninteresting ruin but the view over the picturesque town and of castle is nice.