The Pont des Invalides is the lowest bridge traversing the Seine in Paris.
History
The story of this bridge started in 1821, when engineer Claude Navier conceived a technologically revolutionary bridge that crossed the Seine in one single reach without any point of support in between. The proposed suspension bridge, the construction of which started in 1824, was meant to be erected opposite to the Hotel des Invalides on the site of the current Pont Alexandre III. Navier failed to leave a safety margin on top of his calculations, and the contract to build the bridge was unusually rigid. After Navier's plan had been approved by the privateinvestment company, the contractor could not make changes without approval, and there was no authorization to suggest improvements. The bridge became unsafe after cracking of the anchorages due to natural settling and additional movement after a water main break near the buttresses. The bridge had to be dismantled, and Navier was chastised by a government committee for relying too much on mathematics. He was even compared unfavorably to the accomplishments of British bridge builders. After a settlement between the contractor and investors was reached, the raw materials were reused for other bridges, with designs to be provided by the head investor Alain Desjardins, which were widely seen as less elegant. In response to complaints from the defenders of the Invalides perspective, the Public Services decided to shift the bridge site downriver. Therefore, in 1829, two engineers, de Verges and Bayard de la Vingtrie, completed the construction of a proper suspension bridge supported by two piers in the Seine and three porticos, each 20 m in height. Unfortunately, due to rapidly growing wear on the bridge, its access had to be regulated in 1850. In 1854, the bridge was demolished to be replaced by a new one in time for the upcoming 1855 World Fair in Paris. Paul-Martin Gallocher de Lagalisserie and Jules Savarin used the existing piers of the former suspension bridge and a newly added central pier to build an arch bridge in masonry on the same site. The new pier was adorned with sculptures in two allegorical themes: the Land Victory by Victor Vilain upriver; the Maritime Victory by Georges Diébolt downstream, whereas the two old piers were adorned with sculptures of military trophies bearing the imperial coat of arms, both the work of Astyanax-Scévola Bosio. Despite being stronger, the new bridge still sustained a subsidence between 25 and 30 cm in 1878, and lost two arches during the winter of 1880. The bridge has been quite secure since then and the only modification made in the 20th century was the expansion of its pavement in 1956.
