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 ft) 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 ft) 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 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 Rheinbach, 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 medieval construction.