Isabella of Castile, the sister of Henry the Impotent, notwithstanding the opposition of her brother and the intervention of almost insurmountable obstacles, espoused Ferdinand the Catholic, the king of Sicily, and heir presumptive of the kingdom of Aragon.[18] This marriage, by uniting the two most powerful monarchs of Spain, gave a fatal blow to the prosperity of the Moors, which they had been able to maintain, even in the degree in which it now existed, only through the divisions which had hitherto perpetually prevailed among their Christian opponents. Either of the two enemies, now unitedly arrayed against them, had been singly sufficient {182} to overwhelm the Mussulmans. Ferdinand was alike politic, able, and adroit. He was pliant, and, at the same time, firm; cautious to a degree sometimes amounting to pusillanimity; cunning even to falsehood, and endowed in an extraordinary degree with the power of discerning at a single glance all the various means of attaining a particular end. Isabella was of a prouder and more noble nature; endowed with heroic courage and the most unyielding constancy of purpose, she was admirably qualified for the pursuit and accomplishment of any enterprise to which she might direct the energies of her powerful mind. The exalted endowments of one of these royal personages have been employed to ennoble the character of the other. Ferdinand often played the part of a weak, perfidious woman, negotiating only to deceive; whereas Isabella was always the high-souled sovereign, advancing openly to her purposes, and marching directly to honourable conflict and generous triumph. No sooner had these distinguished individuals secured possession of their respective kingdoms, suppressed all domestic disturbances, and effected peaceful arrangements with foreign powers, {183} than they mutually resolved to concentrate all their efforts for the annihilation of the Mohammedan dominion in Spain.