Pope Eugene IV was elected, and Prospero joined the rest of the Colonna family in rebellion against the new pontiff, who proceeded to deprive the cardinal of all of his benefices.
[5] Colonna, with the aid of his baronial relatives carried off much of the papal treasure, and was excommunicated by Eugene IV prior to his disgorgement.
[5] The aged Colonna changed his vote to Piccolomini by accessus after cardinals Guillaume d'Estouteville and Basilios Bessarion attempted to remove him from the room by force.
Lorenzo Valla was in Colonna's entourage, and Poggio Bracciolini dedicated Da avaritia to him, a book that, in spite of its title, expanded upon the joyous uses of riches.
[15] Another Colonna protégé, the humanist Flavio Biondo, records the restorations and excavations undertaken in the gardens, noting the discovery of extensive marble floors and other remains.
[16] Biondo was inspired to begin his Roma instaurata, the first archaeological topology of ancient Rome, in Colonna's company, when they were on a trip to view the Roman theater at Albano; Biondo refers to Colonna as alter nostri saeculi Maecenas, "for our times another Maecenas", in part for his restorations to his titular church, San Giorgio in Velabro,[17] now largely effaced by modern restorations intended to recapture its medieval ambience.