CASTRES: V. ALBRI, ARCIDIOCESI di.
CASTRIOTA SCANDERBEG, GIORGIO: V. SCANDERBEG, GIORGIO CASTRIOTA DETTO, GIORGIO.
CASTRO, ALFONSO de: V. ALFONSO DI CASTRO.
CASTRO, GUERRA di. — Pope Paul III had granted to his relatives, the Farnese, besides the possession of Parma also that of a small duchy in the Viterbese, called after the main settlement, Castro, situated within the territories of the Papal States. At the time of Urban VIII the Barberini, avid nephews of the reigning Pope, viewed with disfavour the presence of outsiders on the doorstep of Rome; in turn, Odoardo Farnese, Duke of Parma, had various reasons for resentment against the Pope and the new lords. Under these conditions it was easy to find a casus belli, and the war soon turned into a test of the political prestige of the State of the Church, involving all the other Italian States which were glad to strike a blow at ecclesiastical power.