Both sides now embarked on an intensification of the fortress-building spree that had begun in the mid-1590s, enveloping the Republic in a double belt of fortresses on its outer borders (an outer Spanish and an inner Dutch belt). The Dutch fortresses, mostly outside the provinces of the Union of Utrecht proper, were garrisoned with mercenary troops that, though paid for the account of individual provinces, were under federal command since 1594. The Dutch "Staatse leger" (States Army) had therefore become a truly federal army, consisting mostly of Scottish, English, German and Swiss mercenaries, but commanded by a Dutch officer corps. This standing army almost trebled in size to 50,000 between 1588 and 1607.