These prisoners were kept at Norman Cross on the outskirts of Peterborough from 1797 to 1814, in what is believed to be the world's first purpose built prisoner of war camp. The art collection contains an impressive variety of paintings, prints and drawings dating from the 1600s to the present day. Peterborough Museum also holds regular temporary exhibitions, weekend events and guided tours. Burghley House to the north of Peterborough, near Stamford, was built and mostly designed by Sir William Cecil, later 1st Baron Burghley, who was Lord High Treasurer to Queen Elizabeth I for most of her reign. The country house, with a park laid out by Lancelot 'Capability' Brown in the 18th century, is one of the principal examples of 16th-century English architecture. The estate, still home to his descendants, hosts the Burghley Horse Trials, an annual three-day event. Another Grade I listed building, Milton Hall near Castor, ancestral home of the Barons and later Earls Fitzwilliam, also dates from the same period. For two centuries following the restoration the city was a pocket borough of this family. The John Clare Cottage in the village of Helpston was purchased by the John Clare Trust in 2005. The cottage, home of John Clare from his birth in 1793 until 1832, has been restored using traditional building methods to create a resource where visitors can learn about the poet, his works and how rural people lived in the early 19th century. The John Clare Cottage and Thorney Heritage Museum form part of the Greater Fens Museum Partnership, along with Peterborough Museum and Flag Fen. Longthorpe Tower, a 14th-century three-storey tower and fortified manor house in the care of English Heritage, is situated about west of the city centre. It is a scheduled monument, and contains the finest and most complete set of domestic paintings of their period in northern Europe. Nearby Thorpe Hall is one of the few mansions built in the Commonwealth period. A maternity hospital from 1943 to 1970, it was acquired by the Sue Ryder Foundation in 1986 and is currently in use as a hospice. Flag Fen, the Bronze Age archaeological site, was discovered in 1982, when a team led by Dr Francis Pryor carried out a survey of dykes in the area. Probably religious, it comprises a large number of poles arranged in five long rows, connecting Whittlesey with Peterborough across the wet fenland. The museum exhibits many of the artefacts found, including what is believed to be the oldest wheel in Britain.