The Canal lateral a la Loire runs parallel to France's longest river, connecting the country's canal network between the Loire basin and the Seine. But to reach the Briare Canal on the Loire's eastern bank, boats had to cross the river itself -- a harrowing passage during floods, when the Loire's currents could swamp a loaded barge. The river-level crossing near Chatillon-sur-Loire was dangerous enough to justify a colossal investment: an elevated steel channel that would carry the canal cleanly over the river, insulating boats from the Loire's moods entirely. The aqueduct became part of the Canal lateral a la Loire, not the Briare Canal itself, though the two are easily confused. Its purpose was simple and its execution extraordinary -- a bridge not for roads or trains but for water and the boats that float upon it.

The aqueduct was designed by engineers Leonce-Abel Mazoyer and Charles Sigault, but the masonry work -- the fourteen piers and their abutments -- was completed between 1890 and 1896 by the firm of Gustave Eiffel, whose tower had opened in Paris just a year before construction began. The steel channel itself was fabricated by Dayde and Pille of Creil. On September 16, 1896, the boat Aristide, belonging to Ernest Guingamp, made the inaugural crossing, and the aqueduct opened for commercial traffic on the Freycinet gauge, the standard that governed French canal dimensions. Each end of the structure is marked by two ornamental columns modeled after those on the Pont Alexandre III in Paris, lending an unexpected grandeur to what is, functionally, a steel trough full of water.

The dimensions are precise and deliberately modest. The steel channel is 6 meters wide and 2.2 meters deep, allowing boats with a draft of up to 1.8 meters to pass. Including the towpaths on either side, the aqueduct spans 11.5 meters across. A line of lampposts runs along each edge, giving it the appearance of a Parisian boulevard suspended above farmland. Eight sluices allow the channel to be drained in the event of severe freezing -- a practical necessity in the continental climate of central France, where winters can lock the canals in ice for weeks. Below, the Loire flows as it always has, indifferent to the boats gliding overhead. The contrast between the engineered stillness of the canal and the natural current of the river is the structure's quiet poetry.

Commercial barge traffic has declined since the aqueduct's heyday, but pleasure boats now make the crossing in growing numbers, part of a revival of canal tourism across France. The experience is unlike any other waterway passage: the low parapet walls mean that from the deck of a boat you can see the Loire Valley spread out on both sides, the river running beneath you, the countryside stretching to the horizon. The aqueduct lost its title as the world's longest to the Magdeburg Water Bridge in 2003, a structure nearly half again its length crossing the Elbe in Germany. But the Briare Aqueduct remains a registered historic monument, its Eiffel-built piers and ornamental columns a reminder of the era when France's inland waterways were the arteries of commerce and their engineering was treated with the same ambition as any cathedral or palace.