Eifel Aqueduct

The Eifel Aqueduct, constructed in AD 80, was the longest Roman water supply system north of the Alps, carrying water approximately 95 km from the Eifel mountains to Colonia Claudia Ara Agrippinensium (modern Cologne). Built almost entirely underground to prevent freezing, the gravity-fed system included a notable 1,400-metre arched bridge over the Swistbach. It could transport up to 200,000 cubic metres of water daily. After ceasing operation in the 3rd century, calcium deposits up to 40 cm thick formed inside the channels; medieval builders quarried this 'Eifel marble' for altar plates and columns in Romanesque churches across the region.