The Basilica of St. Mary of the Angels and the Martyrs is a titular basilica church in Rome, built inside the frigidarium of the Baths of Diocletian in thePiazza della Repubblica. The Cardinal priest of the Titulus S. Mariae Angelorum in Thermis is William Henry Keeler. The basilica is dedicated to the Christian martyrs, known and unknown. By a brief dated 27 July 1561, Pius IV ordered the church "built", to be dedicated to the the Most Blessed Virgin and all the Angels and Martyrs. Impetus for this dedication had been generated by the account of a vision experienced in the ruins of the Baths in 1541 by a Sicilian monk, Antonio del Duca.