As for the semicircular arch, early examples of it have been discovered in Asia Minor, among the ruins of Phrygian cities; in Acarnania, the most westerly province of ancient Greece; and also in that part of Central Italy where the Etruscans, by their powerful civilization, heralded Rome. It was in Etruria that Rome cradled her infancy, for she borrowed from the Etruscans many of her building methods and many of her civil institutions, both religious and political. Among the gleanings that she harvested we find the round-headed arch, which became a symbol of Roman conquest and colonisation. Perhaps it was employed at Rome for the first time in those great sewers, extant still, which were attributed to the statesmanship of Lucumo Tarquinius, the legendary man of wealth who with his wife and retinue migrated in a splendid manner from Etruria and became a Roman citizen. If the sewers were built about 600 years B.C., then the history of round-headed vaults, as Rome collected from many nations the toll of enlightened obedience, extended over more than a thousand years. In the next chapter we shall try to understand the Roman genius, but here we must recall to mind two preliminary points: one is the aboriginal arch of tree-trunks that Cæsar found in Gaulish bridges (pp. 70, 72), the other is the fact that the Romans left in Britain a version of their round-headed arch that is simpler and more rustic than any other. It was copied frequently by mediæval bridge-builders, and to-day many of the copies are known locally as Roman. Brangwyn represents one of these imitations in Harold’s Bridge at Waltham Abbey. Perhaps this bridge may date from Harold’s time, but it is a feeble thing in comparison with the Roman example near Colne, Clitheroe, whose simple and effective structure is bolder in aspect than the New Port at Lincoln, a genuine Roman gateway. There is but one arch in the Roman bridge near Colne, and its voussoirs have no masonry above them, the footway being protected by large cobbles which are easy to displace when they become outworn. Perhaps the width of this bridge may have been great enough for Roman wheels and British chariots, but I doubt if a coster with his cart would make the crossing. Along the ancient tracks of Lancashire there are many single-arch bridges with a Roman aspect, but without an authentic air of stalwart dignity. The one near Colne looks genuinely Roman, while the others speak to me of a Roman tradition enfeebled in much later times by a rather timid craftsmanship. Mr. C. S. Sargisson has examined these bridges carefully, and from him I have received some excellent photographs. [Illustration: BRIDGE AT WALTHAM ABBEY ATTRIBUTED TO HAROLD]