A book of bridges

by Walter Shaw Sparrow

But this old bridge, with all its charm and interest, is eclipsed as a work of art by the Pont Napoléon, whose gigantic arch, in a very noble curve, spans the rocky and precipitous gorge of the Pas de l’Échelle, along which the furious Gave de Gavarnie pursues a foam-bubbled race against time, sixty-seven metres below the bridge. Here is a masterpiece that rivals the Puente Nuevo at Ronda, thrown across the tremendous chasm of the Guadalvia.[120]

5. The Monnow Bridge at Monmouth.

WAR-BRIDGE AT MONMOUTH

This bluff old gate-tower is a bolder specimen of mediæval work than the smaller one at Warkworth. We are lucky indeed to possess a war-bridge which has suffered so little from time and trade and highway officials. If you compare it with the Brangwyn water-colour of Parthenay Bridge, over the Thouet, you will be better able to put the Monnow Bridge in its proper place as a work of defensive art. The French tower is far and away superior: it has scale and dignity: it is a work of architecture as well as an instrument of war. At Monmouth, how different is the technical inspiration! Not a trace of good design saves the gate-tower from being no more than a weapon for ruthless men. A Peace Society could publish the Monnow Bridge as a fact to prove that slaughtering wars have been more vulgar even than the cruel battles of finance. It is the undefensive parts of this bridge that I admire. The ribbed arches are good ([p. 93]), and in them a slight tentative effort has been made to free the ring of voussoirs from the oscillation sent down through the spandrils when a great weight passes along the footway. “A slight tentative effort,” I repeat, because the archstones have not been made independent from the spandrils.

6. To find arches of this kind we must return to the Pont Valentré at Cahors, which dates from the middle of the thirteenth century. In this noble bridge the voussoirs of all the arches look isolated from the spandrils, as they are rimmed and “extra-dossed.” It was the Romans who invented the “extra-dossed” arch, and they proved that by separating archstones from the spandrils a bridge was relieved from much wear and tear. On the other hand, when archstones are unequal, when they are thicker in their haunches than at the crown, oscillation goes along the full length of a bridge, fatiguing the piers, and causing at times a noticeable shiver, as in the Llanrwst Bridge, designed by Inigo Jones.[121] Even Perronet forgot this effect of repercussion when he built his bridge in the Place de la Concorde at Paris; and ever afterwards he clamped the headers with iron to the interior archstones, as if iron fastened into stone could never become a destructive agent.

The architect of Valentré Bridge was wiser than Perronet, every arch in his work being an elastic bow that moves between two piers without conveying its oscillation beyond these supports. To our modern eyes, no doubt, there are too many arches across the River Lot at Cahors, but this defect seemed necessary in the Middle Ages, and for two reasons. It was regarded as a defensive precaution, because narrow arches were easier to protect from the roadway when an enemy tried to assemble boats under a bridge; and since in the frequent wars of those days a bridge had often to be cut as a final resource against defeat, it was essential that the destruction of one arch should not upset another by the withdrawal of a counterbalancing thrust from one side of a pier. Many piers of a large size were looked upon as particularly needful when the greater lateral thrust of round arches had to be considered in its relation to a bridge cut in a single place. Also, as we have seen ([p. 264]), bridges in the Middle Ages were built very slowly, and as war at any moment might stop the masons, piers were regarded as abutments and made very strong.

This much is known, but none can say why piers were built unreasonably large. Frequent inundations from obstructed rivers were as evidently harmful as weak piers that floods overthrew; and the genius that solved so many problems in church architecture ought to have shown in bridges a riper discretion. Often piers and arches were of the same width—a waste of labour and material, as well as of space in the waterway. Even the Romans, though their piers were less bulky, impeded the current of rivers with too much stone; and to save their work from the floods which they provoked, they built relief bays for spate water above that part of their piers where adequate resistance had been obtained against the lateral thrust of heavy arches.

In the Valentré at Cahors the architect scorned the aid of relief bays, and grew five vast piers from the river-bed; not a courteous thing to do, seeing that the word river in French is a lady-word, “La rivière”—the very sound of it is a sweet compliment to the youthful waywardness of running water. Yet French bridge-masters have sinned against rivers as frequently as we English. If the Valentré had one pier less, how ample and noble the design would be! Even now the design is so virile, so masculine, that we ought to speak of this bridge as we do of a great soldier. The feeble word “it” does not belong to the Pont Valentré. “He” and “him” and “his” are the right pronouns. According to many writers he is the finest military bridge in the world, but comparisons are difficult and risky: they are affected too much by a writer’s moods. One thing is certain—that the Valentré has no superior in his own line. His most celebrated rivals, two bridges at Toledo, in Spain, have a feminine grace; they are too courtly to be typical soldiers. There is another Spanish bridge that ranks high as a fortified work: it dates from the fourteenth century, and, in sixteen pointed arches, crosses the Duero at Zamora. Brangwyn prefers the Toledo bridges, the Alcántara and the Puente de San Martin, because they are lofty as well as spacious, while Zamora Bridge is long and low, like a good many Spanish bridges, both Roman and mediæval.[122]