Francis soon availed himself of the difficulties and dangers of his rival, formed an alliance with the Turks, put forth his old claims, courted the favor of the German Protestants, and renewed hostilities. He marched towards Italy, and took possession of the dominions of the duke of Savoy, whom the emperor, at this juncture, was unable to assist, on account of his African expedition against the pirate Barbarossa. This noted corsair had built up a great power in Tunis and Algiers, and committed shameful ravages on all Christian nations. Charles landed in Africa with thirty thousand men, took the fortress of Goletta, defeated the pirate's army, captured his capital, and restored the exiled Moorish king to his throne. In the midst of these victories Francis invaded Savoy. Charles was terribly indignant, and loaded his rival with such violent invectives that Francis challenged him to single combat. The challenge was accepted, but the duel was never fought. Charles, in his turn, invaded France, with a large army, for that age--forty thousand foot and ten thousand horse; but the expedition was unfortunate. Francis acted on the defensive with admirable skill, and was fortunate in his general Montmorency, who seemed possessed with the spirit of a Fabius. The emperor, at last, was compelled to return ingloriously, having lost half of his army without having gained a single important advantage. The joy of Francis, however, was embittered by the death of the dauphin, attributed by some to the infamous Catharine de Medicis, wife of the Duke of Orleans, in order to secure the crown to her husband. War did not end with the retreat of Charles, but was continued, with great personal animosity, until mutual exhaustion led to a truce for ten years, concluded at Nice, in 1538. Both parties had exerted their utmost strength, and neither had obtained any signal advantage. Notwithstanding their open and secret enmity, they had an interview shortly after the truce, in which both vied with each other in expressions of esteem and friendship, and in the exhibition of chivalrous courtesies--a miserable mockery, as shown by the violation of the terms of the truce, and the renewal of hostilities in 1541. [Sidenote: African Wars.]