There is a tree on a lawn in the new residential area of Vleuten-De Meern. “A black alder”, says archaeologist Erik Graafstal. But in his mind’s eye he sees something else. “There must still be a Roman swamp bridge below.” He points to a football field ahead. “There was a breakthrough of the Rhine around AD 120, leaving a crevasse, an overflow channel.” Walking along the pond at the Lawick van Pabstlaan, he spreads his arms. “This is where the shoreline ran.” Pointing to the north. “That’s where the river flowed, at least a hundred yards wide.”
When Graafstal drives, cycles or walks through Leidsche Rijn, he always sees a place where he and his colleagues from Erfgoed Utrecht excavated parts of the Limes, the northern Roman empire, between 1997 and 2019. The finds – remains of ships, revetments, bridges, quays, roads, watchtowers, jetties – have provided a unique picture of how the Romans managed to survive in a river landscape for three or four centuries.
The tour of places of Roman water management started in the Hoge Woerd museum, built on the remains of a Roman fort discovered in 1940. Graafstal had pointed to a pillar in the museum café. It stands on the site of a small excavation from 2015 that had shown well the water forces the Romans had to deal with. „First we found neat remains from the late 1st century AD, followed by the fire layer from 69, when the Batavians revolted. But underneath there were not the expected remains from 40-41, when the first fort was built, but two thick layers of sand.” Investigation revealed that it was sediment from two massive floods. The solution against further flooding was simple: from then on, when rebuilding fortresses, which they always built close to the river for strategic and practical reasons, the Romans first brought a good layer of soil to act as a mound.
Photo Dieuwertje Bravenboer
Photo Dieuwertje Bravenboer
Photo Dieuwertje Bravenboer
At the Lawick van Pabstlaan, a footpath cuts diagonally through a residential block. It indicates where the Limesweg ran, along which the Romans could quickly move troops. The excavation at this site also told us about the power of the river, explains Graafstal. “In 125, under Emperor Hadrian, the Romans carried out road work to repair damage caused by the Rhine. There has been a breach here over a length of about two hundred meters.”
Over time, wise by trial and error, the Romans understood that sometimes it was better to give the water room. “In case of crevasses, they wouldn’t lead the road again over a dike that closed the overflow channel, to over pole yoke bridges, a kind of swamp bridges.”
Every year the bend moved a meter to the west
Erik Graafstal archaeologist
Throughout the area are countless crevasses. So far, Graafstal and his colleagues have excavated two bridges and located two more. “In the western Netherlands there must have been at least dozens,” he says. He notices that many new gullies were created around the beginning of the era. “Shortly after the Roman general Drusus built a dam at the junction of Rhine and Waal. As an unintended effect, this could have led to all kinds of breakthroughs at Leidsche Rijn.”
About five hundred meters to the east, at Claudiuslaan, a steel plate marks the spot where a watchtower has been excavated. An earlier watchtower stood thirty meters to the east, says Graafstal. “The river was always moving. Every year the bend moved a meter to the west. To keep a good view of the bend, the Romans moved the watchtower after roughly thirty years.”
Read about the behavior of rivers: Meandering rivers? That’s nothing for the Netherlands
Preventing erosion
At what is now called the Augustusweg and the Trajanushof, the archaeologists came across a major work to prevent erosion in a bend. “In the year 100, under Trajan, they reinforced the bank with basalt blocks and built a groyne, a short formwork dam. That groyne had to ensure that the river no longer wears out. The basalt blocks came from near Bonn, some 250 kilometers upstream. That must have been many ship movements.” Apparently that effort had not been enough, because during excavations in 2005, to which the well-known British television program Time Team participated, Utrecht archaeologists discovered a wreck of a Roman freighter near the groyne. “The ship was high on the bank with its prow or stern and was filled with basalt blocks. It was probably sunk deliberately and weighted down with basalt blocks to break the flow even more.”
A reduced replica of the ship partly protrudes from the ground next to the site of the excavation. “We have not fully excavated the ship, which must have been about four meters wide and 27 meters long. Most of it is still in the ground,” explains Graafstal.
This draws attention to another aspect of archeology and water: the water level in the area must be high enough to prevent wood from coming into contact with oxygen and drying out. “After the excavation, the Cultural Heritage Agency of the Netherlands drove monitoring wells into the ground to measure and monitor the storage conditions,” says Graafstal. He looks around for a while, but can’t find any monitoring wells. “They may have stopped monitoring when they saw that everything was okay. I know the level of the locks in the area is being monitored, and it’s still okay. Recently we found archaeological wood nearby and it was in excellent condition even in the top layer. So the ship will be fine too.”