At the age of twenty–six Charles married Isabella of Portugal, a beautiful princess, to whom he was much attached, and who became the mother of his only legitimate son, Philip II, who was born in 1527. That same year Charles was called upon to wage another little war with Francis, who had broken his pledges and formed a league with Henry of England and the Pope. The Spanish armies, under lead of the recreant Constable of Bourbon, overran Italian territories, took and sacked the city of Rome, committing every imaginable excess, and ending by making the Pope himself a prisoner. Although his own army had committed this sacrilege, Charles pretended to be grieved at the event, particularly at the indignity offered to the person of the Pope; but only three years later he had the imperial crown set upon his brow by this same Pope Clement, who had only regained his liberty by the payment of a heavy ransom. The treaty then signed by the hitherto hostile belligerents, called the Peace of Cambrai, was probably hastened by the threatened invasion of western Europe by the Mohammedans under Soleyman the Magnificent; and it was this fear also that caused Charles to treat his Protestant subjects so leniently in Germany, when in Spain they would all have been burned at the stake or put to the sword. But he needed their valiant arms in opposing the Moslems of Turkey in their victorious progress; hence they were temporarily spared, to grow eventually into a body politic of such proportions that, to his sorrow, they eventually overcame him. He, however, vindicated his claim to be considered the champion of Christendom, in 1535, by organizing an expedition against Barbarossa, the pirate king, and liberating hundreds of Christians confined in the dungeons of Tunis. Another attempt upon Algiers, in 1541, resulted in the dispersion of the Spanish fleet by a storm, and disastrous defeat. The year 1536 was made memorable to the citizens of Ghent because, having refused to furnish their quota for carrying on the wars in France, they were treated by Charles as rebels and punished with terrible severity.