Arenberg Castle is a castle in Heverlee close to Leuven in Belgium. It is surrounded by a park.
The site had been the castle of the lords of Heverlee since the 12th century, but this family became impoverished and had to sell the site in 1445 to the Croÿ family from Picardy. Antoon van Croy demolished the medieval castle and started works to build the current castle in 1455 on the site, of which he destroyed all but one tower. Willem van Croÿ completed the works on the castle in 1515, and founded a monastery on the castle grounds for the Benedictine Celestines. The architectural style is in large part traditionally Flemish, with sandstone window frames and brick walls, though it has been structurally altered since 1515 and has elements of Gothic, Renaissance and Neo Gothic architecture. Its large corner towers are typical, once surmounted by a German eagle.
Charles III of Croy was the 4th and last duke, and after his death in 1612 without issue the castle passed to the Arenberg family into which his sister had married, and remained in that family until the First World War.
The first manned gas-filled balloon flight in history took off from the front lawn of the castle on November 21, 1783; the balloonist was professor Jan Pieter Minckeleers.
Even before the First World War, the 8th duke of Arenberg wanted to sell the castle and its grounds to the Catholic University of Leuven, for a reasonable price. During the First World War, the castle and grounds were occupied by the Germans and Austrians. The castle and park were seized by the Belgian government on the outbreak of, and then after the war since the Arenberg family was considered to be German or Austrian due to their close Habsburg connection, monarchs of Austria-Hungary. It took until 1921 for the University to acquire them, becoming an expanded natural sciences and engineering campus in the style of that of an American university. After the partitioning of the University along language lines in 1968, the castle and grounds remained with the Dutch speaking half as one of the main campuses for the new, independent Katholieke Universiteit Leuven. The castle itself is the main building of the Faculty of Engineering and houses lecture rooms and studios for the Department of Architecture, Urbanism and Urban Planning, including the Post-Graduate Centre Human Settlements and the Raymond Lemaire International Centre for Conservation. The building is open to the public. The former Celestine monastery on the castle grounds now houses the campus library, and the addresses of many of the science buildings are on the street named, Celestijnlaan.