Eifel Aqueduct

About

The Eifel Aqueduct was one of the longest aqueducts of the Roman Empire. The aqueduct, constructed in AD 80, carried water some 95 kilometres (59 mi) 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 130 kilometres (81 mi). 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 1,400 metres (0.87 mi) 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.

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 20,000 cubic metres (4,400,000 imp gal) 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.

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.

To protect against frost, most of the aqueduct ran about 1 m (3 ft) 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 70 centimetres (28 in) and a height of 1 metre (3.3 ft), 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.

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.

- Grüner Pütz (Green well) near Nettersheim

- Klausbrunnen (Klaus spring) near Mechernich

- An area of springs in Mechernich-Urfey

- The Hausener Benden in Mechernich-Eiserfey The spring area Hausener Benden, also near Mechernich, is interesting because it was discovered rather late and was put back into use. In 1938, while searching for a drinking water source for Mechernich, the workers encountered the feed line for the aqueduct from this area. The water from the feed was simply connected into the modern water network. So as not to damage the spring, they carried out no archaeological search for the construction around the spring.

Romans preferred drinking water with a high mineral content, preferring its taste to that of soft water. Roman architect Vitruvius described the process for testing a source of drinking water:

Springs should be tested and proved in advance in the following ways. If they run free and open, inspect and observe the physique of the people who dwell in the vicinity before beginning to conduct the water, and if their frames are strong, their complexions fresh, legs sound, and eyes clear, the springs deserve complete approval. If it is a spring just dug out, its water is excellent if it can be sprinkled into a Corinthian vase or into any other sort made of good bronze without leaving a spot on it. Again, if such water is boiled in a bronze cauldron, afterwards left for a time, and then poured off without sand or mud being found at the bottom of the cauldron, that water also will have proved its excellence.

Vitruvius insisted, "Consequently we must take great care and pains in searching for springs and selecting them, keeping in view the health of mankind." The water from the Eifel aqueduct was considered to be some of the very best water in the empire.

Unfortunately, hard water tends to produce calcium carbonate deposits, and all areas of the aqueduct today have a thick layer of limestone -like deposits up to 20 centimetres (8 in) thick. Despite the reduction in the cross-sectional area of the aqueduct caused by these deposits, the aqueduct was still able to provide the necessary quantity of water for Cologne. In the Middle Ages, the layer of "Eifel marble" from the aqueduct was widely reused as building material.

For various reasons, the Eifel aqueduct has very few above-ground sections, unlike other Roman aqueducts, such as the Pont du Gard in southern France :

- The course of the aqueduct was chosen so as to avoid the need for such constructions.

- The water arriving in Cologne had a pleasant temperature due to the insulating properties of the ground.

- In case of war, the aqueduct would be less easily damaged. Nonetheless, there are a few places where bridges or other constructions were necessary. The most notable was an arched bridge over the Swistbach near Rheinbach that was 1,400 metres (0.87 mi) long and up to 10 metres (33 ft) high. Archaeologists calculate that the original bridge had 295 arches, each 3.56 metres (11.7 ft) wide, but the bridge has been reduced to rubble with the passage of the years.