supplied elsewhere, is that the superstructure was of wood.”[43] In other words, this colossal work was a descendant of the earliest tree-bridges, in so far as the footway was concerned. Whether arched timbering was carried from pier to pier to uphold the roadway, as in the bas-relief, is a question of no great moment; the horizontal bearing beams would need support, no doubt, since they had to span openings far wider than the longest trees; and it is useless for us to guess in what way this support was carried to them from the lofty piers, which were built with enormous blocks of stone. The main point is that one phase of bridge-building, whose first models were fallen trees lying astride rivers and chasms, seems to have culminated in the masterpiece of Apollodorus of Damascus. Much inferior work of the same kind, very varied and entertaining, has been common everywhere; some of it belongs to Kurdistan, for example (p. 73); and in the Lledr Valley there is a good Welsh specimen called the Pont-y-Pant, whose wooden footway is primitively rustic, and whose piers are fragments of rock gathered from the river-bed and piled together. I have found at Thirlmere a quaint thing which is partly a dam and partly a bridge. The dam, an undulating wall of unmortared stones, has at equal intervals a few angular openings over which wooden hand-bridges are thrown. It would be easy in a shallow river to make a fish-pool by heaping boulders into a dam of this rude sort, and the completed work would rank no higher than the beavers contests against running water. So I tell myself that many a tribe in the great period of prehistoric art, about 50,000 years B.C., ought to have built for itself a bridge as elementary as the Pont-y-Pant and a perforated dam as uncouth as the one at Thirlmere. From this untutored handicraft we look back again at the great art of Apollodorus, whose vast bridge over the Danube was near the ancient town of Nicopolis. What a long travail in the gestation and birth of infrequent ideas! Even half a million years ago a man of the eagle-beaked tools may have put a boulder under a tree-bridge because the tree was thin and swayed too much on a windy day; half a million years ago, and yet we do not feel ashamed of the Pont-y-Pant! V TREE-BRIDGES WITH TIMBER PILES Let me restate the first periods in their history:-- 1. A windfall tree lying astride a gap in the land. 2. A windfall tree dragged from a wood and put astride a gap in the land, perhaps by a tribe of semi-human creatures directed by a superior mind.