Cynllibiwg (or some variation) was evidently a place name in early medieval Wales. The earliest surviving reference to it is in the Historia Brittonum, which describes a marvelous spring in the regione of Cinlipiuc that has an abundance of fish despite not being fed by a stream. John Edward Lloyd notes that this Cinlipiuc appears to be one of the various district names created by adding the element -wg to a personal name, in this case an unknown Cunalipi or Cynllib. The Domesday Book refers to a place called Calcebuef, which rendered ten shillings; one editor suggests this is a corruption of Cynllibiwg and that it derives ultimately from the name of Saint Cynllo. However, Lloyd connects this name instead to the cantref of Buellt. The Red Book of the Exchequer, a mainly 13th-century compila