Harold, the Last of the Saxon Kings Book VII: The Welch King by Edward Bulwer-lytton

On the height called Pen-y-Dinas (or "Head of the City") forming one of the summits of Penmaen-mawr, and in the heart of that supposed fortress which no eye in the Saxon camp had surveyed [163], reclined Gryffyth, the hunted King. Nor is it marvellous that at that day there should be disputes as to the nature and strength of the supposed bulwark, since, in times the most recent, and among antiquaries the most learned, the greatest discrepancies exist, not only as to theoretical opinion, but plain matter of observation, and simple measurement. The place, however, I need scarcely say, was not as we see it now, with its foundations of gigantic ruin, affording ample space for conjecture; yet, even then, a wreck as of Titans, its date and purpose were lost in remote antiquity.

The central area (in which the Welch King now reclined) formed an oval barrow of loose stones: whether so left from the origin, or the relics of some vanished building, was unknown even to bard and diviner. Round this space were four strong circumvallations of loose stones, with a space about eighty yards between each; the walls themselves generally about eight feet wide, but of various height, as the stones had fallen by time and blast. Along these walls rose numerous and almost countless circular buildings, which might pass for towers, though only a few had been recently and rudely roofed in. To the whole of this quadruple enclosure there was but one narrow entrance, now left open as if in scorn of assault; and a winding narrow pass down the mountain, with innumerable curves, alone led to the single threshold.