De Tomp, tower mill ruin in Achel, Belgium

De Tomp is a 15th-century windmill in Hamont-Achel, Belgium, preserved as a protected monument. The structure features a circular brick tower with thick walls and stands on slightly elevated ground surrounded by marshy terrain.

De Tomp is the remnant of a tower mill built in the first half of the 15th century, probably by the lords of Grevenbroek. It was damaged by a storm in 1596 and repaired, but was taken out of use before 1630 and replaced by a wooden post mill, which burned down in 1800. In 1968 the ruin was wrongly restored as a castle tower; only in the 1990s was it identified as a mill by comparison with other tower mills.

The name De Tomp refers to the truncated mill tower, a stump, which is how the ruin is known locally. The mill was probably built by the lords of Grevenbroek, and after storm damage in 1596 it was repaired but taken out of use before 1630, replaced by a wooden post mill that burned down in 1800. Visitors today see the brick stump in the Lange Els nature area near the Warmbeek.

De Tomp stands on a slightly raised mound in the marshy Lange Els nature area, close to the Warmbeek. The ruin is reached on foot through the reserve; the ground around the mound is wet, so waterproof footwear helps outside dry spells. The stump rises about 20 m after restoration, with walls roughly 1.75 m thick around an inner diameter of about 4.60 m.

For decades, the structure was mistaken for a castle tower ruin until experts in the 1990s identified it as a grain mill by comparing it with similar mills from the same period. This misidentification even led to an incorrect restoration in the 1960s.