CHACÓN (Ciacconius), ALONSO. - Born at Baeza (Granada) in 1540, died at Rome on 15 February 1599. He entered the Order of Friars Preachers and was prior of the convent of St. Thomas in Seville; having come to Rome in the time of Gregory XIII (1572-85), he was a penitentiary at St. Mary Major. He lived in Rome on the Pincio, where he established a library and a museum recalled by Macarius (Hagioglypta; Paris 1856, p. 2). He was among the visitors of the cemetery galleries (of the Giordani) that came back to light in 1578, and he had copies made of the paintings, sarcophagi and inscriptions that had turned out poorly (J. Wilpert, Die Katahombiensemälde und ihre alten Copien, Freiburg im Br. 1917), as well as the others of the cemeteries of Priscilla, of St. Valentine, of Domitilla, and of the underground of St. Nicholas in Carcere, copies preserved in Cod. vat. lat. 5409.
From an examination of his correspondence in the Chigi library, Mabillon recognized that C. had in mind two works, one De antiquitatibus Romanis and the other Bibliotheca a plurimis antea auctoribus dispersim institute et collecta, deinde ab aliquot in epitomem redacta (J. Mabillon, Museum Italicum, I: Iter Italicum litterarium, Paris 1724, p. 96). Of this work, vol. I up to the letter E was printed at Paris; only in 1831 did G. B. De Rossi rediscover the manuscript (Bull. di arch. crist., 1st series, 2 [1864], p. 88). Also posthumous is his best-known work, Vitae et res gestae Summorum Pontificum a Christo Domino usque ad Clementem VIII nec non S. R. E. Cardin. M. Alfonsi Ciacconii Biacensis, Ordinis Praedicatorum et Apostolici Poenitentiarii, published in Rome in 1601 under the care of his nephew Alfonso Ciacconio. Although superseded in various respects, it is still indispensable for consultation. The work received successive additions under the care of F. Cabrera Morales, A. Vittorelli, F. Ughelli, G. Allandro, L. Wadding, C. Becillo; A. Oldoini extended it in 1677 down to Clement IX, and M. Guarnacci in 1751 down to Clement XII.