PIERS OF BRIDGES, 114, 200, 264, 316, 338, 341, 342, 353, 354. There are other references also, but the reader will be able to follow the history of piers from the natural bridge of stepping-stones through the many changes and defects mentioned in the text. To-day, with the rapid improvements in airships and aeroplanes, new armoured piers will have to be designed, strong enough to bear the great weight of a roofed superstructure of armour-plate steel, yet not thick enough to obstruct rivers. Now that bridges are as vulnerable as Zeppelin sheds, engineers have an excellent chance to serve their countries well by inventing new and powerful bridges. How to protect piers--at least as much as possible--from direct artillery fire is one very difficult problem; how to protect them from falling shells and bombs is another. When London is fitted adequately with new defensive bridges her river will be as impressive as a fleet of super-Dreadnoughts. See also “Abutment Piers.” PIERS, CRISS-CROSS, Gaulish, 70; in Kashmír, 71-3; in North Russia, 73. PIERS, FOUNDING, 99, 197, 251-2, 341-2. PIGS, in China, sacrificed to rivers when bridges are in danger from floods, 69 _footnote_, 248. PINGERON, M., his remarks on Loyang Bridge, 127. PIRANESI, GIAMBATTISTA, 1720-78, 193, 197. PISA, her chapelled bridge, 209. The late Mr. S. Wayland Kershaw wrote as follows in 1882: “The most remarkable bridge chapel abroad is the one dedicated to Santa Maria del’ Epina on the side of the bridge over the Arno at Pisa, erected about 1230. Built of the rich stone and marble of the district, it is ornamented with niches and figures, and, though renovated and repaired, still presents a graceful appearance.” POINTED ARCHES AND VAULTS, in Nature, 6 _footnote_; in Egypt of the Fourth Dynasty, 155-6; in Babylonian work, 275 _footnote_; at Arpino, 156; in early French bridges, 6 _footnote_, 86-93. POITOU, in its relation to ribbed arches in bridges, 95. POLO, MARCO, 128, 210, 310, 313. PONS ÆLIUS, 194-5. PONS ÆMILIUS, 193 _footnote_. PONS AURELIUS, 197. PONS CESTIUS, 196-7. PONS FABRICIUS, 195-6. PONS GRATIANUS, 196. PONS LAPIDEUS, 140. PONS MILVIUS, 197. PONS NERONIANUS, 197. PONS PALATINUS or Senatorius, 192-3. PONS SALARUS, 191. PONS SELMIS, 178. PONS SUBLICIUS, 41, 64, 136, 140. PONS TRIUMPHALIS, 197. PONS VATICANUS, 197. PONT AU CHANGE, a Paris bridge, 224. PONT AUX MEUNIERS, a Paris bridge, 224. PONT D’ARC, a Nature-made bridge, 6. PONT D’AMBROISE, a Roman bridge, 82. PONT DE BROEL, a Flemish war-bridge, 290. PONT D’ESPAGNE, a modern French bridge, 278. PONT DES CONSULS, a mediæval bridge at Montauban, 27, 254-6. PONT DE VERNAY at Airvault, see the plate facing page 96. PONT DU GARD, Roman bridge-aqueduct, 83, 167-75.