ZUCCHETTO (biretum, submirtale, subbirretum, pileolus, calotta, Soli-Deo). — A half-spherical cap, worn white by the pope, red by cardinals (granted in 1464 by Paul II; to regular cardinals in 1591 by Gregory XIV), purple by bishops (1867 by Pius IX), black by abbots and those with privilege or indult (CIC 325; 625; 811, 2).
It was in use during the 14th century, as seen beneath the tiara of Pope Clement VI (d. 1352) in the sepulchral monument at La Chaise-Dieu. Its use spread during the 15th century (cf. Ordo Romanus XIV, 118; XV, 144: PL 78, 1272, 1351) and became general in the 16th and 17th centuries. In the 15th and 16th centuries it covered the entire occiput, gradually reducing to its present small form. It may be worn during Holy Mass outside the Canon, but not during Eucharistic processions or public exposition of the Blessed Sacrament. It is also worn under the mitre, called submirtale.