Clas (ecclesiastical settlement)

A clas (Welsh pl. clasau) was a native Christian church in early medieval Wales. Unlike later Norman monasteries, which were made up of a main religious building supported by several smaller buildings, such as cloisters and kitchens, a clas was normally a single building. The building was run by a community of clergy and headed by an abod. Clasau were autonomous and were administered locally.

Following the Norman invasion of Wales in the late 11th century, many of the clasau of south Wales became dependencies of religious houses in England. This resulted in several sites becoming part of the Benedictine or Augustinian orders, or built upon in the following centuries by Norman churches.