After the French recapture, Calais was on the frontier, only a short distance from the Spanish-held stronghold of Gravelines. A strong citadel was built on the west side of the town, incorperating the medieval castle into one corner. Calais was occupied by the Spanish from 1596 to 1598.
When the town was returned to France, Henry IV had Errard improve the citadel. It was rectangular with 4 bastions, one of which encapsulated the old castle. There were gates on the south and east fronts, both defended by demi-lunes.
The town was surrounded with a bastioned trace sometime in the early 16th century, although the medieval defences were left intact as an inner defence. Vauban consolidated the defences of the citadel in the 1690's, which consisted mainly of razing the castle and replacing it with a more conventional bastion.
By kjfitz @ 2009-02-11 09:14:17