sentences:  In the 1950s the NBR archive acquisitions included the collections of Sydney Pitcher (medieval architecture and vernacular buildings); Helmut Gernsheim (photographs of tombs in St Pauls Cathedral and Westminster Abbey) as well as continued recording of architectural details such as glass, fixtures and fittings, woodwork and sculpture.The 1950s also saw the start of aerial photography to discover and record ancient sites, as more intensive agriculture, forestry and gravel extraction threatened historic remains on "marginal land".The NBR was merged with the Royal Commission on the Historical Monuments of England (RCHME) in 1963.