Ivo de Vesci, Baron of Alnwick, built the first parts around 1096, and the castle was rebuilt in stone in 1157. The Percy family acquired it in 1307, and Henry Percy and his son rebuilt it as a border fortress in the 14th century, leaving the Abbot's Tower, Middle Gateway and Constable's Tower.
The principal rooms sit in a much-rebuilt shell keep made of ten tightly packed towers, one of the earliest English castles built without a square keep. In the 18th century Robert Adam, James Paine and others worked for the Percys, producing mostly Strawberry Hill Gothic interiors. From 1854 to 1865 Anthony Salvin remodeled the castle in a medieval style for the 4th Duke.
The castle has stood in films, including as Hogwarts in the early Harry Potter films. The 12th Duke of Northumberland's family lives in part of it, and it is open to the public in summer.

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