 In 1603 King Philip III decided to make use of the clause of the treaty of 1557 that allowed Spain to fortify any part of the Island of Elba and on 22 October of the following year he ordered his viceroy, Juan Alonso Pimentel de Herrera, to build a fortress on the island.Construction of Fort San Giacomo at Porto Longone began in March 1605.It had barracks for 2,000 men.