Claud Lyuarch hen (Llywarch Hen’s dyke) is named in the boundary clause of an early medieval charter contained in the twelfth century Book of Llandaff. The charter grants an estate at Llan-gors (Brycheiniog), and purports to have been made a King Awst and his sons in the early- to mid-eighth century. The place-name is a clear reference to the Llywarch Hen of Welsh poetic tradition, and a case has been made for the poems having been written at Llan-gors sometime between the eighth and tenth century (Sims- Williams 1993). The dyke can be identified on the ground as a penclawdd (head-dyke); a land boundary that separated lowland infield from the unenclosed upland pastures. Thus, whilst the dyke was a prominent feature in the landscape it is unlikely to have served as a defensive earthwork. Nevertheless, it can be argued that Llywarch Hen’s dyke was more than just a convenient feature with which to define an estate. Rather, the earthwork and the oral traditions associated with it performed a didactic role that reinforced knowledge of the physical extent of the estate and of the status and power of those who held it.