ture. In fact, the larger the curve of the arch, the stronger the arch will be. In order to construct such a form, and until the final stone at the top of the arch (the “keystone”) has been placed, the arch has to be supported by a system of scaffold- ing or “centering.” Once the keystone has been positioned, however, the resulting form is much stronger than the earlier arching techniques that preceded it. (See Section I: Art Fundamentals for a diagram outlining the various types and details of vaulting systems.) The Romans made many advances on the simple arch as well. A series of arches butted up against each other were used to create a barrel vault, which could be taller and wider than a post-and- lintel structure or a corbeled vault. Two barrel vaults could be crossed at a ninety degree angle, which resulted in a groin vault. This structure transferred the thrust of the vault’s weight down to freestanding piers, rather than solid walls, which insured greater flexibility in terms of shap- ing space. This form would be the basis for many important later innovations, and it was key to the development of structures as sophisticated as the Gothic cathedrals. [For a discussion of how arches and the forces on them work, see http:// www.youtube.com/watch?v=CdNYTjXJPKE.] Pont du Gard: Analysis The Pont du Gard is an example of Roman archi- tecture found at Nîmes (ancient Nemausus), Bust of Roman statesman Marcus Agrippa. The Pont du Gard was long believed to France. This example, far from the Italian pen- have been built by Agrippa between insula, shows the geographic breadth of the 20–16 BCE, but recent excavations Roman Empire. It also helps explain one aspect suggest that it may actually have of the Romans’ success and why they were able been built in the first century CE. to expand their reign so widely. As the Romans conquered a new area, they did not simply force the local population under their control. They were careful to provide positive advantages, such as new construction projects like bridges and roads, in order to win the favor of the indigenous commu- nity. The Pont du Gard is a perfect instance of this. It is an aqueduct bridge built to bring clean water to the people of Nîmes. The bridge transported clean water from springs at Uzès thirty-one miles away and provided each of the approximately 50,000 citizens of the city with a hundred gallons per day. The Pont du Gard and the aqueduct system for Nîmes were long believed to have been built by the Roman statesman Marcus Agrippa between 20–16 BCE. Recent excavations suggest that it may actually have been built in the first century CE. Regardless of its true date of construction, the bridge is one of the best preserved in the Roman world. As the water in the system traveled from the spring outside the city, it was brought through an array of channels to the center of town. Simple gravity brought the flow through these channels, which are set variously throughout the system, below ground, on low walls, or across the bridge as seen here. Overall, the water fell only fifty-six feet from the elevation of the spring to the fountains at Nîmes. As the system reached the gorge of the Gardon River, it was necessary to construct a bridge. This maintained the elevation of the channel and kept the water smoothly flowing through the system. The resulting structure is the highest Roman aqueduct bridge constructed. It was designed as a three- story structure, 880 feet long and 160 feet high. Each of the large arches of the lower stories spans eighty-two feet and is built of stone blocks weighing two tons each. No mortar or clamps were used 14–2015 • USAD ART RES 20 OURCE GUIDE • REVISED 62 PAGE.