Gravelines

Historique et description

A site occupied by fishermen since the 7th century, Gravelines is a new town founded by the Count of Flanders, which serves as the outer harbour in Saint-Omer and which was surrounded by a first defensive wall in the form of an earth wall. After a siege by the English in 1383, the urban wall was replaced by grassed ramparts and brick walls. It was also endowed with a castle intended to oversee the locks of the river Aa and its first line of hydraulic defences. Between 1528 and 1535, Charles Quint had the castle reconstructed and modernised it with the addition of artillery installations and a bastion. The lock of the Bourbourg canal was reconstructed at the same time and transformed into a flushing lock, capable of emptying away the estuary sludge during the marsh at each equinox. His son, Philippe II of Spain, transformed the urban wall from 1558: a modern rampart with six great bastions and a glacis covering the medieval walls. The bastion of the castle was transformed and included in the hexagonal urban wall. The Italian engineers Ogiati, Thebaldi and Saluberto supervised all the construction carried out during the reign of Philippe II. His successors expanded the moats, added a covered way and a second exterior moat in 1637. They also had the fort Saint-Philippe constructed at the mouth of the Aa, channelled to protect the mooring facility from 1640, whereupon a second fort rapidly followed the first. The canal of Aa, meanwhile, was excavated from 1639, but French attacks in 1644 and 1652 interrupted this construction, which had to be continued up until 1658.
Captured by the France in 1658, Gravelines was redesigned in the twenty-two years that followed. The intention was to transform it into a site included in the first line of defence. It was integrated into the Pré Carré in 1678. During this period, Spanish works were restored and further construction was undertaken. The ramparts were subject to significant renovation: the width of the protective wall was tripled with the construction of ravelins, counterscarps, projections and a covered way. Vauban stepped in for the first time in 1683 by reconstructing an artillery installation at the castle, which he turned into an arsenal. In 1699, he set out a significant flushing lock, which was installed on the Aa, and which allowed peripheral flood defences to be open or closed. This lock allowed the dredging of the channelled portion of the Aa and a corresponding increase in its flow. A vast hornwork protected this lock.
However, the scope of Gravelines would not extend beyond the second line of the Pré Carré. Accordingly, the construction program laid out by Vauban was only implemented progressively, based on the funding available. All this meant it was not until midway through the 18th century that they were completed with the deepening of the Aa channel in 1740. During this period, the former ravelins and counterguards were transformed and new ones were also added. The 19th century saw work proceed on an overall upgrade, but one which left the plan of the ramparts and flood defences in place. This upgrade involved reshaping the parapets, transforming the vaults of the bastion flanks, revegetating exterior works and restoring the hydraulic system. All the machines were replaced and the flushing lock of Vauban was entirely reconstructed.