An Engineer's Triumph
The Pont du Gard is the most famous segment of a nearly 50-kilometer-long aqueduct system built by the Romans in the 1st century AD. Its purpose was to carry water from a spring near Uzès to the Roman city of Nemausus, now Nîmes. The entire aqueduct descends only 17 meters over its full length, which demanded extraordinary precision from its builders. This translates to an average gradient of about 34 centimeters per kilometer, or a slope of 1 in 3,000. Some sections of the aqueduct have a gradient as shallow as 1 in 20,000.
To achieve this, Roman engineers relied on simple but effective instruments. The chorobates, a 20-foot-long wooden bench with plumb lines and a water channel, was used to establish level surfaces. For sighting straight lines and right angles, they used a groma. These tools allowed them to plot a course that snaked through the landscape, using gravity alone to move an estimated 40,000 cubic meters of water to Nîmes every day. The water took nearly 27 hours to travel from the source to the city. The bridge portion itself, which crosses the Gardon River, shows this precision, descending a mere 2.5 centimeters over its 275-meter length.