The medieval Welsh prose classic known as The Mabinogi survives complete in two important fourteenth-century manuscripts and in a thirteenth-century fragment. This paper looks at ways in which the four interlaced tales, incorporating elements of much earlier myth and legend, are also recorded and reflected in the Welsh landscape, especially in place names and place name clusters that reference the tales. Using the analogy of Western Apache place tales, it suggests that the place names and the landscape of the tales served (and perhaps still serve) as reminders both of the cultural significance of the tales and of the importance of the themes that they explore. It also looks at the ways in which Anglo-Norman and English regimes overlaid that significance with tangible demonstrations of their own power and authority. Finally, it explores how the geographic reach of The Mabinogi served to reinforce a growing sense of Welsh cultural unity during a period when political unification may have seemed within reach.