Peter Ernst, count of Mansfeld, born July 20, 1517, died in Luxemburg, May 22, 1604. The greater part of his life was spent in the service of the emperor Charles V., and of his son Philip II. of Spain, who employed him in various important military and administrative capacities. He took part in the war against France in 1552, was captured, and remained a prisoner till 1557. Having been appointed governor of Luxemburg, he maintained that province in tranquillity at a time when the other provinces of the Netherlands were a prey to civil and religious commotions. In 1592 he succeeded the duke of Parma as governor general of the Netherlands; but two years afterward he retired to Luxemburg, with the title of prince of the empire.
Ernst, natural son of the preceding, born in 1585, died near Zara, Dalmatia, Nov. 20, 1626. He was educated by his godfather, the archduke Ernest of Austria, and for his military services to the emperor Rudolph II. and Philip III. of Spain was legitimated by the former. But having been denied the dignity and estates of his father, which had been promised to him, he embraced Calvinism, and subsequently became one of the most active enemies of the house of Austria, by which he was called the Attila of Christendom. At the commencement of the thirty years' war he joined the elector palatine Frederick, elected by the Protestants king of Bohemia, and vigorously opposed the imperial forces in that country and also on the Rhine, where he ravaged the territories of the Catholic princes, and became a terror to his enemies. Though repeatedly beaten, he came forth so formidable from every defeat, that, when fighting for a desperate cause and lying under the ban of the empire, he found himself courted at the same time by the kings of Spain, France, and England, and the republics of Holland and Venice. In 1625 he "succeeded in raising subsidies in England, and landed in Holland with considerable reinforcements, with the design of invading the hereditary possessions of the house of Austria. Defeated by Wallenstein at Dessau in April, 1626, he nevertheless pursued his march to Hungary, to effect a junction with Bethlen, the Protestant prince of Transylvania. But being unable to join his ally, he formed the design of reaching England by the way of Venice, and died on the march.