Carvajal's career as a soldier in Europe spanned forty years and a half-dozen wars. Fighting in Spain's Imperial armies—the famous "tercios"—he served under Charles V's principal commanders in the Italian Wars: Pedro Navarro, Fabrizio Colonna, and the illustrious "Gran Capitán", Gonzalo Fernández de Córdoba. He took part in the memorable Spanish victory at the Battle of Pavia in 1525 and acquired a small fortune when the Imperial armies sacked Rome two years later.