Introduction
The Pont du Gard, a massive bridge-aqueduct, was built in what is now southern France to span the Gardon River and deliver potable water to the city of Nemausus. While the underground pipe system connecting the ancient city to its water supply is gone, the bridge remains today. The structure is a testament to Roman ambition, ingenuity, and architectural skills.
Ancient Rome's unparalleled engineering prowess and skill at urban planning are why so many of its structures remain from antiquity. Completing major construction projects in every corner of its empire helped the government maintain order as the marvels they erected awed residents and tangibly benefited the population.
The Romans constructed over 258 miles of aqueducts. Reliable water sources were vital for drinking, cultivating crops, raising livestock, and bathing. Aqueduct planning was challenging because the Romans had to rely on gravity to keep water moving over miles, which meant that making precise measurements and design was critical. The stakes were high considering the scope of the projects and the necessary exertion of labor.
Location
The Pont du Gard is located near the present-day town of Vers-Pont-du-Gard on the Gardon River, in France's southern region of Occitanie near the Mediterranean Sea. The bridge is the signature component of the Nemausus Aqueduct, which channeled water south from the natural springs of Fontaine d'Eure near Uzès to Nemausus during the Roman Empire.
The builders had to cross the Gardon River, which runs east of the city, because there was no easily accessible water source for the aqueduct closer to Nemausus. The city sits on a vast plain with the rolling foothills of the Massif Central Mountains on its western border. That densely forested and treacherous terrain would have made tunneling impractical.
Design and Construction
The long-held consensus concerning the Pont du Gard was that Marcus Vipsanius Agrippa oversaw its construction at the direction of his father-in-law, Emperor Augustus, in 19 BC. Historians proposed that it was just one of the many projects Agrippa led in his administrative role as part of the emperor's public works campaign.
Based on recently unearthed artifacts found in the riverbed at the construction site, and a tunnel system that the bridge completely bypasses, historians now believe the Pont du Gard was built between 40 and 60 AD, during the reign of Claudius.
Scholars differ on the project's timeline. Some propose it took about three years to complete, while others contend that it took as long as 15 years. The bridge's construction required between 800 and 1,000 laborers.
It is estimated that the bridge cost around 30 million sesterces due to the complexity of its design and the need for fortification against the raging Gardon River.
The Pont du Gard was a multi-function tri-level structure in ancient Rome, serving as both a bridge for travelers and an aqueduct. It still stands 160 feet tall and 21 feet across at its widest point. It was originally 1,180 feet long, and featured a total of 64 arches of varying lengths. Each is a recessed curved stone structure that unites two piers.
The lowest level features six arches that each stand 72 feet tall. They total 466 feet long and 20 feet thick. The widest is in the center, allowing the freest flow of water to minimize wear and tear from the current.
The middle level consists of eleven 66 foot tall arches that reach 794 feet in length. The piers are 13 feet thick. This level served as the bridge for traffic crossing the river.
The upper level originally consisted of 47 arches that were 23 feet tall and totaled 902 feet in length, however, only 35 of the aqueduct's top arches still exist. The top also served as the canal for traveling water. The variation of arch placement across the three levels strengthened the bridge by effectively distributing weight.
The aqueduct has an average grade of 0.39 inches over the bridge, allowing water to flow into the basins, called "castellum divisorum," at its conclusion in Nemausus. Water was then dispersed through the city via a widespread network of underground pipes. The system supplied fountains, bathhouses, and private homes.
The aqueduct spanned 31 miles from its source spring to Nemausus. Despite its long and winding path that crossed multiple rivers and uneven terrain, the entire system only varies 41 feet in height from its highest to lowest point.
The Romans built the Pont du Gard using Shelly limestone, a sedimentary rock composed of fossil fragments. The builders took the stone from the Estel quarry, which sat on the banks of the Gardon River, some 2,300 feet from the construction site. Quarrymen excavated the rock using pick axes and metal corners. They then cut the stone to precise specifications, as each piece was preplanned to fit like the pieces of a mosaic.
The highly coordinated endeavor relied on smooth communication and attention to detail. Each building block featured a serial number, designating it for a specific spot on the bridge. Researchers estimate the Pont du Gard contains 50,400 tons of limestone with a volume of 740,000 cubic feet.
Construction Methods
The project's chief architect and key construction figures are currently unknown. Typical of the period, either the city of Nemausus or a wealthy benefactor would have likely commissioned the construction.
The build team consisted of both contractors and skilled laborers, and an initial engineering team would have planned the project and completed the survey of the area using:
- A groma, which was a pole with wooden pieces mounted at the top, forming a cross with four right angles. Each tip of the cross had a plumb line hanging down to the ground. The surveyor would lay out straight lines and signal to an assistant, who would then place poles marking the placement of construction pieces.
- Chorobates were precursors to bubble levels and spirit levels. They were 20 foot planks of wood with a leg at each end. A plumb line dangled at each end of the plank. The legs attached to the plank with notched diagonal rods. The surveyor would adjust the plank by repositioning the legs along the notches. Once the two plumb lines matched, the surface was level.
The surveyor then transcribed his measurements on wax tablets which were used to compile blueprints to be used by the laborers.
The Romans built the bridge without using clamps or mortar; the stones were cut with such precision that gravity held them in place.
Each arch was assembled around a wooden frame. The builders would add wedged-shaped stones to fill out the structure. Once the keystone, or central stone, was placed, the arch was locked and the frame was removed. The weight was then evenly distributed to hold the entire unit in place.
The largest stones, placed at the bridge's base, weigh almost 6 tons each. They arrived at the construction site from the quarry by boat. The Romans positioned the massive stones using cranes and pulley systems to move and lift the snuggly-fitting stones on the middle and top levels. Hoisting the large stones used for the lower level required a man-powered treadmill.
Like modern-day construction, the builders also assembled a scaffold to support the bridge and enable ongoing work as it grew taller and taller. There are stones incorporated into the bridge's structure that served as anchor points for the scaffolding, further proving the Romans' capacity for complex planning and project management.
After completion, the anchor stones allowed workers to remount the scaffolds to carry out maintenance projects or routine repairs to the structure.
Internal Design
Considering the subtle gradient of the aqueduct, the builders had to minimize obstructions and friction inside the channel. The interior walls featured dressed masonry and a concrete floor. Workers then coated the entire tunnel with stucco that featured tile and pieces of pottery.
The conduit was then slathered with olive oil and topped with maltha, a concoction of lime slurry, pork grease, and juice from unripe figs. The coating guarded the channels and enhanced water flow.
Function During the Empire
The Pont du Gard was a costly but necessary undertaking for the Romans. Nemausus came under their control in 28 BC, and was a valuable territory that helped Rome establish a foothold in Hispania and fuel its expansion.
Members of Julius Caesar's legions who served in the Nile campaigns received land in Nemausus to farm, and during the early first century AD, the city's population ballooned to 20,000 as it prospered, outgrowing the Nemausus Fountain, its initial water source.
The Romans utilized the Eure in Uzés as the source for the aqueduct to supply Nemausus. The system involved 31 miles of pipes and the construction of the Pont du Gard. Historians estimate the aqueduct delivered nearly 9 million gallons of water to Nemausus every day!
Maintenance
Keeping the water flowing was vital for maintaining order and tranquility within the city. Circitores were the workers tasked with aqueduct upkeep and maintenance.
The water from the source spring was rich in dissolved calcium carbonate, which reacted with the bridge's limestone. Over time, it laid down calcium deposits through the system, disrupting the water flow.
In addition, the miles-long network was susceptible to penetration by plants. While the vegetation itself would disrupt the channel, it also fostered algae growth that rendered the water undrinkable.
The channels were approximately six feet tall to make maintenance easier. The circitores had to crawl through the tunnels on the Pont du Gard and across the entire aqueduct system, clearing sediment buildup, removing plants, and scrubbing the calcium deposits from the stone.
After the Fall of Rome
Even before Rome fell, maintenance of the Pont du Gard aqueduct and bridge was sacrificed to focus on defense against incursions from invaders.
Water flow was significantly restricted by the late fourth century AD due to root invasion of the pipe system and sediment buildup along the Pont du Gard. The lack of routine cleaning and necessary repairs allowed debris to clog the system, choking off the water supply by the sixth century AD.
The Pont du Gard remained largely intact over the next several hundred years. Despite frequent flooding and violent waters, the bridge endured because the Romans' securely anchored structure resisted breakdown. As common with many Roman constructs, even ones within Italy, parts of the bridge were plundered and repurposed for contemporary building projects at the time.
As French society grew, the king granted toll rights to fiefs in the region during the thirteenth century. Their use of the Pont du Gard to collect funds spurred them to preserve and maintain the structure. The bridge remained largely intact until the 1620s, when the Duke of Rohan removed stones from the second level to widen the crossing, allowing the transport of artillery and cannons.
A restoration project in 1703 replaced missing stones and repaired cracks. Then, in 1743 a companion bridge was built along the lower level to accommodate heavier traffic.
Napoleon III directed further preservation in the late 1850s. The bridge's piers were fortified with concrete, the stone was replaced, and the aqueduct was separated from the bridge. Stairs were built allowing visitors to access the bridge and turn the structure into an early tourist destination.
The Pont du Gard Today
Modern-day Nîmes in France embraces its Roman history as Nemausus and is home to some of the most striking surviving ancient structures outside of Italy. The Pont du Gard is one of the most prominent marvels of Roman engineering still standing. In just the last 75 years, it experienced flooding in 1958 that reached the bridge's second tier, in 1998 that damaged nearby bridges, and in 2002.
Interestingly, French legend claimed the bridge was the work of the devil because it seemed implausible the structure could endure the tumultuous river. The speculation of people living hundreds of years after the construction underlines the extent of the Romans' mastery of engineering and construction.
UNESCO designated the Pont du Gard as a World Heritage Site in 1985 due to its cultural significance and excellent preservation. It is the tallest aqueduct the Romans ever built.
Over one million people visit the site each year, and the French government and UNESCO have taken proactive steps to regulate foot traffic and minimize wear-and-tear on the structure, in order to limit further erosion that could compromise the bridge.
