Petworth House was originally a 12th century fortified manor house, founded by Queen Adeliza of Louvain. In 1309, Henry, Lord Percy of Alnwick founded the stone castle, when King Edward II granted him, a license to crenellate. In the late 16th and early 17th century, the earls of Northumberland extended and repaired the castle. In the late 17th century, Charles Seymour, duke of Somerset, absorbed the fortification in the construction of a magnificent country mansion, which then received considerable 19th century alterations, by Anthony Salvin. The chapel, with its Early English Gothic windows, is the only surviving complete part of the medieval castle but restoration work has also revealed, a medieval outer wall, an external mullioned window and an original spiral stair turret. 4 miles west is Lodsworth Castle and 6 miles south-east is Pulborough Castle.