The Eifel Aqueduct was one of the longest aqueducts of the Roman Empire.
The aqueduct, constructed in AD 80, carried water some from the hilly Eifel region of what is now Germany to the ancient city of Colonia Claudia Ara Agrippinensium (present-day Cologne). If the auxiliary spurs to additional springs are included, the length was . The construction was almost entirely below ground, and the flow of the water was produced entirely by gravity. A few bridges, including one up to in length, were needed to pass over valleys. Unlike some of the other famous Roman aqueducts, the Eifel aqueduct was specifically designed to minimize the above-ground portion to protect it from damage and freezing.
History
Before the building of the Eifel Aqueduct, Cologne got its water from the Vorgebirge aqueduct, which had its source in the springs and streams from the Ville region to the west of the city. As the city grew, this aqueduct was no longer able to provide enough water of sufficient quality: the springs contained a small amount of silt in the summer, and sometimes even ran dry. A new aqueduct was built to bring water from the springs of the Eifel into the city.
The Eifel aqueduct was built in the northern part of the region. The construction is of concrete with stones forming an arched covering. It had a maximum capacity of approximately of drinking water daily. The aqueduct provided water for the fountains, baths and private homes of Colonia Claudia Ara Agrippinensium. The aqueduct remained in use until about 260, when the city was first plundered by the German tribes. After this date, it was never brought back into operation, and the city obtained its water from the old Vorgebirge Aqueduct.
Course
The aqueduct began at a spring in the area of Nettersheim in the Urft river valley. It then travelled along the valley to Kall, where it had to overcome the divide between the Maas and the Rhine. The Roman engineers chose this spot because they were able to overcome the divide without resorting to a tunnel or a pump. The aqueduct then ran parallel to the northern Eifel Mountains, crossing the Erft near Kreuzweingarten (in the Euskirchen district) and the Swistbach with an arched bridge. In Kottenforst, northwest of Bonn, it passed through the Vorgebirge highlands. Finally, it ran through Brühl and Hürth before arriving in Cologne. Other springs in the region that met Roman quality and quantity guidelines were also equipped with aqueducts to feed the main line.
Architectural aspects
To protect against frost, most of the aqueduct ran about below the Earth's surface. Archaeological excavations show that, at the lowest level, the Roman engineers had placed a loose layer of stones. On this base, they set a concrete or stone U-shaped groove for the water and, over this, cut stones and mortar were used to build a protective arch.
For the concrete work and the arch, the engineers used boards to build the form. Impressions of the wood grain remain in the concrete 2,000 years later. The aqueduct had an inner width of and a height of , so a worker could enter the tube when necessary. The outside of the aqueduct was plastered to keep dirty water out. At several locations, a drainage system was set up alongside the aqueduct to keep ground water away. Smaller streams crossed the aqueduct through culverts: one, very near the source, is still well-preserved.
The inside of the aqueduct was also plastered with a reddish mixture called opus signinum. This mixture contained lime as well as crushed bricks. This material hardened under water and prevented leakages to the outside. Small cracks were sealed with wood ash, which was strewn over them the first time the aqueduct was set in operation.
Roman spring constructions
Several springs in the area were fitted with constructions to aid their direction into the aqueduct. The first is at the source, Grüner Pütz near Nettersheim. The most studied is the "Klaus fountain" at Mechernich. This site has been archaeologically reconstructed and preserved. The constructions at the various springs were designed to fit in with the characteristics of the area and would meet today's technical requirements.
There were four major areas of springs: Grüner Pütz (Green well) near Nettersheim Klausbrunnen (Klaus spring) near Mechernich An area of springs in Mechernich-Urfey The Hausener Benden in Mechernich-Eiserfey