It is certain that most of the Roman bridges were built with timber. Thousands of trees were cut down when a paved road was constructed, so that cheap material for bridge-building was always at hand when the road was carried over ravines and rivers.[50] Besides, if a great many stone bridges had been built by the Romans, in Britain and elsewhere, many remains of the piers would have been found in all big rivers. We know, too, that the Romans were tolerant in their attitude to native bridgemen, since the criss-cross piers of the Gauls outlived the Roman Empire by many centuries. We know not, neither can we learn, how the Romans themselves made timber bridges. Even their Pons Sublicius, a sacred monument, hallowed by historical traditions and by its connection with religious ceremonies, was described imperfectly. To this day experts quarrel over its technique and over its position on the Tiber. Colonel Emy has tried to reconstruct it, but his attempt differs from that of Canina, and we cannot choose between them. The utmost we can say is this--that the Pons Sublicius was a tree-bridge resting on piles, and dating from the times of Ancus Marcius, who reigned from B.C. 640-616. If the chief priests did not build it, they certainly kept it in repair, always using wood with a pious regard for a venerated past; and with their help it existed as late as the reign of Constantine (A.D. 306-337), when it was mentioned in the “Notitia,” and when a bridge was named after it at Constantinople. But the Pons Sublicius became obsolete as a highway for traffic, and then a good understudy bridge of stone--the Pons Lapideus--was built close at hand, and was known sometimes as Pons Sublicius, a title of honour. Sir William Smith believed that these bridges were outside the city, beyond the Porta Trigemina, and that the wooden one was built by Ancus Marcius in order to connect the town side of the Tiber with a new fortress erected on the Janiculus.