But the extraordinary interest of these islands lies in the abundance of prehistoric forts and of very early Christian buildings. The greatest of the forts is Dun Conor on Inishmaan, with walls of dry masonry eighteen feet in thickness; but by far the most famous is Dun Angus on Inishmore which, built on the edge of a steep cliff, needed no protection that way, but turned landward a semicircular front of four vast ring fences of stone--the innermost eighteen feet in height. Between the second and third walls is a chevaux de frise formed by sharp, jagged stones set endwise, very difficult to pass over in times of peace. We have it under Dr. Healy's own hand that an archbishop broke his shins there. This fort might have seemed defence enough for the island, but it is studded over with duns--one of them, Dun Eochail, is only half an hour's walk from the pier, and being set high was once utilized for a lighthouse station. To reach it gives one some idea of the island economy, for half a dozen high-piled walls of loose stone have to be crossed or knocked down. There are no gates in these fields; to let in a cow you "knock" the wall, and then pile it again. But you will not easily knock the walls of Dun Eochaill. The outer ring is only some eight foot high and six wide, but the inner circle rises sixteen foot, and may be twelve in thickness. Who built these fortresses, no man can say; probably that early race whom the Milesians superseded. Yet the population of Aran is by no means the little dark type; many fair-haired women, many a red-headed man are among them, and not a few of almost giant stature. It is not surprising, since for many centuries the O'Briens of Clare were overlords of the islands, and the Clan Dalcais were Milesian, if any ever could claim that title. Generally speaking, too, Aran is more in touch with Clare than with Connemara; though it serves as an intermediate centre for the traffic in poteen--illicit whisky--distilled in creeks and bogs along Galway Bay. Aran brings its turf from Connemara and carries them limestone in exchange. Stand on Dun Eochaill, the most commanding point, and you may see the two shores, Clare and Connemara, so near, yet so different in their peoples, and you shall have one of the noblest views in Ireland: southward, away past Loophead and the Shannon mouth to the great mountain promontory of Brandon in Kerry; northward, past the Twelve Pins to Mweelrea and Croaghpatrick and Achill even. Or if, as happened when I saw it last, the view is obscured with driving mist, still you may have a glint of sun between showers to fling a rainbow across the wide water; and you may watch a squall of wind and rain pass flickering over the sound, raising a patch of whitening foam where its fierce edge strikes the surface.