RING OF AN ARCH, the compressed arc of voussoirs, 264; the lower surface of a ring is called the soffit of an arch. In some bridges the voussoirs form a double or a triple ring, 305, and _footnote_. Two very fine bridges of this sort, in my collection of photographs, are the Pont de Vernay at Airvault, 12th century, and the Pont Saint-Généroux over the Thouët, also in Deux-Sèvres, 13th and 14th centuries. Another monument to be studied is the reputed Roman bridge at Viviers over the Rhône, built mainly with small materials. Whether Roman or Romanesque, the structure of the arches has great interest, and a large photograph is sold by Neurdein, 52 Avenue de Breteuil, Paris. RIVERS, how their violence has given lessons to bridge-builders, 181. ROADS, ANCIENT BRITISH, 22; Roman, 139, and _footnote_; they and bridges circulate all the strife in the overland enterprise of mankind, 4, 14-52; types of society are as old as their systems of circulation, just as women and men are as old as their arteries, 13; mediæval roads in England, 51, 52. Many of them were a survival of the Roman empire, in which the construction of highways was a military and political necessity. The genuinely mediæval roads connected new towns with the main or ancient thoroughfares, which had traversed Roman Britain from her principal colonies, London and York, to the other settlements. “The roads of England,” says Thorold Rogers, “are roughly exhibited in a fourteenth century map still preserved in the Bodleian Library, and are identical with many of the highways which we know familiarly. In time these highways fell out of repair, and were put in the eighteenth century under the Turnpike Acts, when they were repaired. But comparatively little of the mileage of English roads is modern. What has been constructed has generally been some shorter and easier routes, for in the days of the stage-coaches it was highly expedient to equalize the stages.” ROANNE, PONT DE, its length and its cost, 356. ROBIN HOOD BALLADS, their rustic charm is repeated in some old English bridges, 9, 44. ROCHE PERCÉE, LA, at Biarritz, natural arched opening, 151. ROCHE TROUÉE, LA, near Saint-Gilles Croix-de-Vie, 151. ROCHESTER BRIDGE and her Chapel, 243-6. ROCK-BASINS, their formation by the erosive power of glaciers, 152, and _footnote_. ROCK-BRIDGES, or bridges made by Nature, 6, and _footnote_, 150-3. ROGERS, THOROLD, PROFESSOR, on mediævalism and industrialism, 47; on mediæval roads, 52; see also “Roads.” ROMAN GATEWAYS to defend bridges, 176-7, 272. ROMAN GENIUS, 23-5, 26-7, 30, and Chapter III. ROMAN CASTLES OR TOWERS to defend bridges, at Mérida, 182, at Alcantarilla, 367-8. ROME, ANCIENT, her bridges, 193 _et seq._ RONDA AND HER BRIDGES, 183, 280, and _footnote_.