The duke of Alba's 700-mile march to the Netherlands at the head of 10,000 veteran Spanish troops in 1567 marked a turning point in European history. It established a Rubicon for Spanish imperialism: a barrier that, once crossed, transformed the political situation in northern Europe and, with it, the prospects of Hapsburg hegemony on the Continent. It also constituted one of the most remarkable logistical feats in European military history, celebrated in art, prose, verse, and proverb.
The decision to march arose from the combination of two separate developments: the spread of Protestant ideas—Lutheran, Anabaptist, and above all Calvinist—throughout the Spanish Netherlands despite savage persecution by the central government in Brussels, and the mounting opposition of some noble members of that central government to the policies decreed by their absentee sovereign, Philip II. Until 1559 the Hapsburg king had ruled his vast empire from Brussels, but in that year he departed for Spain, leaving his half sister, Margaret of Parma, as his regent. In his absence, since Philip refused to heed their political advice, a group of Netherlands nobles led by Count Lamoral of Egmont and Prince William of Orange searched for an issue that would broaden their local support and force the king to listen. They chose religious toleration. Although at this time none of the aristocratic leaders was Protestant, they refused to enforce the laws against heresy, and the number and daring of the Protestants in the Netherlands rapidly increased.