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Eifel Aqueduct

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   The route of the Eifel aqueduct, with its average slope.
   Enlarge
   The route of the Eifel aqueduct, with its average slope.

   The Eifel Aqueduct was one of the longest aqueducts of the Roman
   Empire. It shows the great skill of the Roman engineers, whose level of
   technical achievement was lost in the Middle Ages and regained only in
   recent times.

   The aqueduct, constructed in AD 80, carried water some 95 km (60 miles)
   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 km (80 miles). 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 m (0.87 miles) 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 20,000 m³ (4.4  million UK
   gallons) 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.
   In Buschhoven, near Bonn, a small section of the aqueduct is preserved.
   Enlarge
   In Buschhoven, near Bonn, a small section of the aqueduct is preserved.

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 Mountain, 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

   Reconstructed aqueduct near Mechernich-Vussem
   Enlarge
   Reconstructed aqueduct near Mechernich-Vussem

   To protect against frost, most of the aqueduct ran about 1 m 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  cm (28  inches) and
   a height of 1 m (3.3  feet), 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 passages: 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

   The spring at Grüner Pütz is marked by a Roman pool.
   Enlarge
   The spring at Grüner Pütz is marked by a Roman pool.

   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 fountain) 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.

Roman demands for water quality

   This portion of the aqueduct at Euskirchen Kreuzweingarten shows the
   calcium carbonate accretion on the sides of the channel.
   Enlarge
   This portion of the aqueduct at Euskirchen Kreuzweingarten shows the
   calcium carbonate accretion on the sides of the channel.

   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." (De architectura, 8,4,1,
          trans. Morris Hickey Morgan, 1914)

   Vitruvius insisted (8,3,28), "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 cm (8 inches) 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.

Above-ground sections

   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.
     * By construction underground, the aqueduct was protected from
       freezing.
     * 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 m (0.86 miles) long
   and up to 10 m (32.8 feet) high. Archaeologists calculate that the
   original bridge had 295 arches, each 3.56 m (11.7 feet) wide, but the
   bridge has been reduced to rubble with the passage of the years.

   A smaller arched bridge crossed a valley near Mechernich. This was some
   10 m (32.8 feet) tall and 70 m (230 feet) long. The archaeological
   remains were in good enough condition here that a partial
   reconstruction was built to show how the original must have looked.

Roman aqueduct construction

   Construction of the aqueduct placed great demands on the capacities and
   knowledge of the Roman engineers. The Romans occasionally suffered
   problems of low-quality work on large projects, as witnessed by Sextus
   Julius Frontinus, lead official for water resources in the city of
   Rome, who wrote:

          "No other construction requires greater care in its building as
          one that is to contain water. Therefore it is necessary to
          supervise all aspects of such a project with great
          conscienciousness—proceeding fully in accord with the rules,
          which everyone knows, but only few actually follow."

Cost of building

   Considering the amount of surveying, underground building, and
   bricklaying involved, a construction of this size could not be built
   all at once. Instead, the engineers divided the entire construction
   site into individual building areas. Through archaeological research,
   the boundaries of these building areas have been determined. For the
   Eifel aqueduct, they were 15,000 Roman feet long (4,400 m or 2.7 miles
   in modern units). It has further been demonstrated that the surveying
   took place separately from the building, as is in fact the rule today
   in large construction projects.

   For each metre (3.3 feet) of aqueduct, approximately 3–4 m³
   (100–140 ft³) of earth had to be dug up, followed by 1.5 m³ (50 feet³)
   of concrete and bricklaying, along with 2.2  m² (24  feet²) of plaster
   sealant. The complete labour expense is estimated at 475,000 man-days:
   with about 180 possible construction days in the year due to weather
   conditions, 2,500 workers would have worked 16 months to complete the
   project. The actual construction time appears to have been even longer,
   since this estimate leaves out the question of surveying and production
   of the building materials.

   After construction, the building trenches were filled in, the surface
   flattened, and a maintenance path built. The maintenance path also
   served to delimit areas where farming was not permissible. Other Roman
   aqueducts show similar facilities. The aqueduct to Lyon, France was
   marked with the following inscription:

          "By command of Emperor Trajanus Hadrianus Augustus, no one is
          permitted to plough, sow, or plant within the space determined
          for protection of the aqueduct".

Roman surveying

   After a good location for the aqueduct was selected, it was necessary
   to guarantee a constant slope downwards in its course. Using devices
   similar to modern levels, the Roman engineers were capable of
   maintaining a slope as small as 0.1 percent—one metre of fall for every
   kilometre of aqueduct. In addition to the slope, it was necessary for
   the various building sections to be able to join up, while still
   maintaining a constant downward slope.

   The Roman constructors of the Eifel aqueduct carefully made use of the
   natural fall of the land. If the work from one segment arrived too high
   for the next segment, they built a small pool into the course to calm
   the falling water.

Roman concrete

   The concrete used for the Eifel aqueduct was a combination of lime,
   sand, stones, and water. Boards were used to make a form into which the
   concrete was packed. Modern tests of the quality of the concrete show
   that it would pass current standards. This particular concrete is
   called opus caementicium in Latin.

Operation of the aqueduct

   Maintenance personnel could enter into the channel of the aqueduct
   through shafts like this one.
   Enlarge
   Maintenance personnel could enter into the channel of the aqueduct
   through shafts like this one.

   For the 180 years of the aqueduct's use, from AD 80 to 260, the
   aqueduct required constant maintenance, improvement, cleaning, and
   freeing from limestone accretions. Maintenance was facilitated by
   regular maintenance shafts, through which a worker could descend into
   the aqueduct. Additional maintenance shafts were built at the sites of
   repairs and at the boundaries between building segments. There were
   also open pools at points where various springs ran together so that
   maintenance personnel could keep an eye on problem areas.

Distribution of water in ancient Cologne

   For the last few kilometres before the ancient city, the aqueduct left
   the ground and was supported by an aqueduct bridge approximately 10 m
   (33 feet) high. This additional construction enabled water to be
   delivered to the higher-lying areas of the city through pressurised
   pipes. The pipes at the time were made of lead plates bent into a ring,
   either soldered together or with flanges to bind the individual pipe
   sections together. The Romans used bronze fixtures as taps.

   Incoming water arrived first at the various public fountains of the
   city, which were always in operation. The fountain network was so dense
   that no resident had to travel more than 50 m (164 feet) to get water.
   In addition, various public baths and private homes, as well as public
   toilets were provided with water. Waste water was collected in a
   network of canals under the city and led out into the Rhine. One
   section of the Roman sewer system is open for tourists under Budengasse
   Street in Cologne.

The aqueduct as a stone quarry

   This column in the Bad Münstereifel church of SS. Chrysanthus and Daria
   was made out of the calcium carbonate deposits in the aqueduct
   Enlarge
   This column in the Bad Münstereifel church of SS. Chrysanthus and Daria
   was made out of the calcium carbonate deposits in the aqueduct

   The Eifel aqueduct was destroyed by Germanic tribes in 260 during an
   attack on Cologne, and was never brought back into operation, even
   though the city continued to exist. In the course of the migration of
   the various tribes through the region, aqueduct technology fell out of
   use and knowledge. The entire aqueduct remained buried in the earth
   some 500 years, until the Carolingians began new construction in the
   Rhine valley. As this area has relatively little naturally occurring
   stone, the aqueduct became a favoured place for obtaining building
   materials. Transportable sections of the aqueduct were used to build
   the city wall around Rhinebach, for instance. Some of these sections
   still have the sealing plaster from the aqueduct intact. Thus all of
   the above-ground sections, and a good part of the underground
   construction as well, were dismantled and reused in mediaeval
   construction.

   Particularly desirable as a building material were the limestone-like
   accretions from the inside of the aqueduct. In the course of operation
   of the aqueduct, many sections had a layer as thick as 20 cm
   (8 inches). The material had a consistency similar to brown marble and
   was easily removable from the aqueduct. Upon polishing, it showed
   veins, and it could also be used like a stone board when cut flat. This
   artificial stone found use throughout the Rhineland and was very
   popular for columns, window frames, and even altars. Use of "Eifel
   marble" can be seen as far east as Paderborn and Hildesheim, where it
   was used in the cathedrals. The Danish cathedral at Roskilde is the
   northernmost location of its use, where several gravestones are made of
   it.

   Medieval legend held that the aqueduct was an underground passage from
   Trier to Cologne. According to the legend, the Devil had bet the
   architect of the Cologne cathedral that he could build this tunnel
   faster than the cathedral could be erected. The architect took the bet
   and drove the men to work with great haste. One day, the construction
   workers broke into the aqueduct, where flowing water could be seen. The
   Devil's giggling is said to have driven the architect to suicide by
   jumping from the half-finished cathedral tower. Supposedly, the
   architect's death (and not the lack of funds) was the cause of the
   centuries-long delay in the completion of the construction.

   A few mediaeval writings on the aqueduct lost sight completely of the
   original purpose of the construction. Some say that it carried not
   water, but wine to the city, for example, the Gesta Treverorum of
   Maternus, Bishop of Cologne, (4th century) and the Hymn to Saint Anno
   of the 11th century.

Tourism

   The hiking trail along the Eifel aqueduct is marked with a distinctive
   logo.
   Enlarge
   The hiking trail along the Eifel aqueduct is marked with a distinctive
   logo.

   The Römerkanalwanderweg (Eifel aqueduct hiking trail) runs for
   approximately 100 km (62 miles) along the aqueduct's path from
   Nettersheim all the way to Cologne. Public transport links are good,
   allowing the trail to be walked in various stages. It may also be used
   as a bike trail. There are approximately 75 information stations along
   the way, providing an excellent view of the aqueduct.

Legacy

   Archaeological research on the Eifel aqueduct started in the 19th
   century. CA Eick was the discoverer of the farthest source from Cologne
   at Grüner Pütz near Nettersheim (in 1867). Systematic study of the
   aqueduct was carried out from 1940 to 1970 by Waldemar Haberey. His
   1971 book is still a suitable guide along the course of the
   construction. In 1980, archaeologist Klaus Grewe completely mapped out
   the location line and added it to the official German topographic map.
   His Atlas der römischen Wasserleitungen nach Köln (Atlas of Roman
   Aqueducts to Cologne) is a standard work for researchers in Roman
   architecture.

   The Eifel aqueduct is a very important and valuable archaeological
   site, particularly for the study of Roman surveying, organizational
   ability, and engineering know-how. It is also a poignant symbol for the
   loss of technical knowledge during the decline of civilisations that
   between the Middle Ages and more recent times, no better use was found
   for the aqueduct than as a stone quarry. The Roman level of technology
   in this area was not equalled until the 19th and 20th centuries.
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