Among the most elegant and enduring of Roman structures based on the arch is the Pont du Gard at Nîmes, France (13.9), built about 15 c.e. when the empire was nearing its farthest expansion (see map, p. 344). At that time Roman industry, commerce, and agriculture were at their peak. Engineering was applied to an ambitious system of public-works projects, not just in Italy, but in the outlying areas as well. The Pont du Gard functioned as an aqueduct, a structure meant to transport water, and its lower level served as a footbridge across the river. That it stands today virtually intact after nearly two thousand years (and is crossed by cyclists on the route of the famous Tour de France bicycle race) testifies to the Romans' brilliant engineering skills. Visually, the Pont du Gard exemplifies the best qualities of arch construction. Solid and heavy, obviously durable, it is shot through with open spaces that make it seem light and its weight-bearing capabilities effortless.