Syon Park is the 56.6 hectare (139 acre) garden of Syon House, the London home of the Duke of Northumberland in Isleworth in the London Borough of Hounslow. It was landscaped by Capability Brown in the 18th century, and it is Grade I listed by English Heritage under the Historic Buildings and Ancient Monuments Act 1953 for its special historic interest. The 56.6 hectare main gardens are a Site of Borough Importance for Nature Conservation, Grade I, and the flood meadows next to the River Thames are a biological Site of Special Scientific Interest (SSSI) and a Site of Metropolitan Importance for Nature Conservation.