Opened in 1896, the Briare Aqueduct in France remains one of the grandest navigable aqueducts in the world, stretching 662 meters to carry the Canal Latéral à la Loire directly over the Loire River. Before its construction, canal barges had to cross the actual riverbed of the Loire, a notoriously dangerous task due to unpredictable floods, treacherous quicksands, and severe seasonal low water levels that frequently halted trade for months at a time. To bypass the unpredictable river entirely, engineers Léonce-Émile Mazoyer and Gustave Eiffel designed a massive elevated waterway.
The key engineering breakthrough was the construction of a continuous steel trough masonry-supported bridge. Instead of traditional stone arches that would absorb water and leak under immense hydrostatic pressure, the aqueduct uses a welded sheet-steel channel weighing more than 13,000 tonnes when filled with water. The steel trough is supported by 14 stone piers anchored deep into the riverbed.
Using steel allowed for precise thermal expansion joints and airtight riveting, preventing leaks despite thermal swings across seasons. According to Archimedes' principle of displacement, the total weight exerted by the aqueduct on its supporting piers remains constant whether a barge is present in the trough or not, because an entering vessel displaces an exact volume of water equal to its own weight. This predictable static load allowed engineers to optimize pier thickness and river flow dynamics beneath, creating an enduring masterpiece of 19th-century civil engineering.