High Quality Content by WIKIPEDIA articles! Harmondsworth Great Barn (also known as Manor Farm Barn) is a medieval tithe barn on the former Manor Farm in the village of Harmondsworth, in the London Borough of Hillingdon, England (previously part of the historic county of Middlesex). It stands just north of Heathrow Airport. Built in the early 15th century by Winchester College, it is the largest timber-framed building in England and is regarded as an outstanding example of medieval carpentry. It was described by the English poet John Betjeman as the "Cathedral of Middlesex". A similar though smaller barn is part of the Manor Farm complex in Ruislip.