CHACÓN (Ciacconius), ALONSO. - Born in Baeza (Granada) in 1540, died in Rome on February 15, 1599. He entered the Order of Preachers and was prior of the convent of S. Tommaso in Seville; having come to Rome at the time of Gregory XIII (1572-85), he was a penitentiary at S. Maria Maggiore. He lived in Rome on the Pincio, where he formed a library and a museum recorded by Macarius (Hagioglypta; Paris 1856, p. 2). He was among the visitors to the cemetery galleries (of the Jordani) brought to light in 1578, and he had copies made of the paintings, sarcophagi, and inscriptions that turned out poorly (J. Wilpert, Die Katakombengemälde und ihre alten Copien, Freiburg i. Br. 1917), like the others from the cemeteries of Priscilla, S. Valentino, Domitilla, and the underground of S. Nicola in Carcere—copies preserved in Cod. Vat. Lat. 5409.
From the examination of his correspondence in the Chigiana library, Mabillon recognized that C. had in mind two works, the 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). Vol. I of said work up to the letter E was printed in 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 Although superseded in various respects, it is still of indispensable consultation. The work received subsequent completions under the care of F. Cabrera Morales, A. Vittorelli, F. Ughelli, G. Allandro, L. Wadding, C. Becillo; A. Oldoini extended it in 1677 up to Clement IX, and M. Guarnacci in 1751 up to Clement XII.