Prjects by French engineer-officers from he time of occupation ( 1794-1814) provided the guidelines for the latest mdernization of the foprtress, when this had regained importance as "the key yo Belgium" in the United Kingdom of William I ( 1815-1839). The Lage Fronten between the bastion Holsteyn and the Maas were completely renewed. The existing works were for the greater part demolished, to be replaced by for basions, designated A,B,C and D, which were linked up by a walled earthwork. This line was protected by a moat that could be filled with water via the Jeker channel, a masonry-clad counterscarp, three ravelins, a few redoubts, and a coverd way. Parts of these New Bossche Fronten have escaped demolition. Saved from destruction for the greater part was Fort Willem, built on the slopes of the Caberg mountain in the years 1815-1818.It is a walled earthwork of pentagonall shape, with two casemates, protected by a dry moat, with a masonry-clad, counterscarp and a coverd way. Ring galleries along the full lenght in scarp and counterscarp cover the moat on either side. The fort commanded not only the forefield in the north, but, in cooperation with the fort Sint-Pieter, it could set up a cross-fire before the Hoge Fronten, between the Tongersepoort and the Brusselsepoort.