The next proposal to build a fortification on the island was made by the Italian military engineer Antonio Maurizio Valperga in 1670. He proposed a roughly hexagonal fort with a hornwork, in the Dutch style of fortification. The proposal was criticized by the Order's engineers, and a third proposal was drawn up by the Flemish military engineer Carlos de Grunenbergh in 1687. Grunenburgh's proposal consisted of a fort with four bastions and a ravelin, surrounded by a ditch, covertway and faussebraye.