When the senior line of the Medici family died out the Ducal title was passed to Cosimo, who then married Eleonora Alvarez de Toledo, daughter of the Spanish viceroy. Gradually he increased his power and territory. Pope Pius IV conferred the title of Grand Duke on him and for the rest of his life he ruled as a despot over Florence and Siena. Not fully accepted by European monarchs, he tried to outdo them as a patron of the arts.

Source: Leo van de Pas