Haller, Medieval architectural heritage monument in Monschau, Germany.

The Haller is a tower castle from the 12th or 13th century on a steep rock opposite Monschau Castle. Its residential and defensive tower is enclosed on three sides by walls up to 2.5 metres thick. The eastern and northern bases of the tower show no edges, suggesting the tower base was cut from the rock.

The Haller is thought to predate Monschau Castle; the castle's founders moved across the Rur because the Haller site offered no room to expand. A 17th-century watercolour after an older engraving shows the tower still roofed at the 1543 capture of Monschau. A 1570/71 rent-master's account records that parts of the Haller were dismantled to raise the Eselsturm, with the front wall and slate roofing kept for reuse.

The tower was held by the prince's household, not the townspeople: a 1612 witness statement records that the Haller was maintained and guarded by the prince and his ancestors since time immemorial without ever burdening the citizens. From the second half of the 17th century it served as a powder magazine, with a guardhouse on top.

The Haller stands on a steep rock opposite Monschau Castle, above the town; the tower base appears cut from the rock itself, with no edges on its eastern and northern sides. The surrounding walls, up to 2.5 m thick, run on three sides. Sturdy shoes are advisable on the rock and the slope.

The building served as both a fortress and a lookout point over the valley and surrounding area. Its high position allowed views that stretched far across the landscape.