But it must be remembered that in Spain the Renaissance was never a movement from within; rather its causes were external and political. In 1504 Naples had been conquered by Spain, and at the same time the Sicilies had become an appanage of the House of Aragon. Many Spaniards of position were attracted to Italy to take part in the wars, and with them travelled native artists. At the same time Italian artists came to Spain. Another influence was the close relation which at this time existed between Spain and Rome. Then a thriving trade communication arose between the cities of the two countries, and especially was this so between the prosperous harbours of Barcelona and Genoa. The impulse of art is curiously interbound with economic causes; interchange of trade inevitably results in interchange of culture. The charm of the new style arose from its novelty; it inspired imitation and suggested new theories of art. It found an expression chiefly in the direction of decoration, where the old sumptuousness was united with elegance and delicacy of execution. Thus the Renaissance entered Spain by numerous channels. We find many Spanish nobles employing Italian workmen to decorate their palaces; for instance, Rodrigo de Mendoza entrusted the ornamentation of the castle of Calahorra to Genoese workmen in 1510. Italian marble-cutters were occupied in the production of sumptuous monumental tombs, of which some were carved at Genoa, while a still greater number were executed in Spain by Lombard and Florentine artists summoned thither for the purpose. The mural monument of Archbishop Mendoza in Seville Cathedral was executed by Miguel of Florence about 1509, and by him too is the terra-cotta relief over the Puerta del Perdon, representing the Expulsion of the Money-changers from the Temple and the Annunciation, between the large figures of St. Peter and St. Paul. The monument of P. González de Mendoza in the Capilla Mayor of Toledo Cathedral, with the Madonna in the lunette, is absolutely Florentine, and is perhaps the work of Andrea Sansovino. The Marquis de Tarifa, while on a journey to Palestine in 1520, ordered at Genoa the tomb-monuments of his parents, Enriquez and Catalina de Ribera, the richest examples of Renaissance sculpture, which are in the University Church of Seville. The altar of the Capilla de Exalas, in the cathedral of the same city, which was erected by del Río in 1539, is also of Genoese workmanship. The new style was adopted in decorative sculptures applied to doorways, façades, windows, &c.; there are numerous examples, and especially is this so in the Cathedral of Toledo, which furnishes a museum of Renaissance work.