Mazarin's policies also added Alsace (though not Strasbourg) to France. He settled Protestant princes in secularized bishoprics and abbacies in reward for their political opposition to the Habsburgs, building a network of French influence as a buffer in the western part of the Empire. In 1657, he made an attempt to get Louis XIV elected as Holy Roman Emperor. In 1658 he formed the League of the Rhine, which was designed to check the House of Austria in central Germany. In 1659 he made peace with Habsburg Spain in the Peace of the Pyrenees, which added to French territory Roussillon and northern Cerdanya—as French Cerdagne—in the far south as well as part of the Low Countries.