The construction of this Roman aqueduct has presumably started around year 19 BC and the aqueduct has been carrying water approximately 500 years.
The difference in level between the spring at Uzrs and Nîmes is 56 feet over a distance of 31 miles - that means an average slope of 21 inches per mile.
The average slope between the spring and Pont du Gard (10 miles) is 42 inches per mile and between Pont du Gard and Nîmes (21 miles) the average slope is 1 foot per mile. On a few spots only 4,5 inch per mile!
The amount of water to be transported used to be 5 - 8 million US gallons every day and night corresponding to 160 - 210 gallons per inhabitant of Nîmes.
The variations of slopes on the aqueduct have a logical explanation. Constructing the aqueduct with a uniform slope of 21 inch per mile consequently should have raised the level of the bridge by 15-16 feet, so that the total height of the bridge would have been 176 feet. The present height of 160 feet represents the highest construction from the Roman era. The aqueduct therefore represents the most outstanding of what technically could be obtained at that time. For the same reason you'll find Pont du Gard over-dimensioned but still harmonic.
Pont du Gard were later used by the local inhabitants to cross the river Gardon and gradually the columns on second floor were demolished to make room for crossing by pack asses. The stability of the bridge became worryingly weak and the missing stones were replaced.
In 1743 a decision was made in order to expand Pont du Gard with a road on the one side of the bridge so crossing without risking life became a reality. At the same time it became possible to enjoy the beauty of this great monument.
Pont Du Gard is built in 3 floors and has a total height of 160 feet corresponding to an 18-floor apartment house.
Pont Du Gard is one of the three star sights in France and paying a visit whenever possible is strongly recommended.