The papal crown, or tiara, was traditionally worn by the popes until the pontificate of Pope John Paul I. Like many ceremonial items, the papal tiara developed over time. Since the pope is also the bishop of Rome, he wears a miter for liturgical ceremonies.
Since the pope is also the pastor of the universal church, some kind of headdress was adopted to be worn outside of liturgical functions to highlight his authority (particularly in temporal affairs). The papal tiara is first mentioned in the account of the life of Pope Constantine (708-715) in the Liber Pontificalis; here it was called a “camelaucum,” which was part of the Byzantine court dress and looked like a “papal cap” made of white cloth; Pope St. Gregory the Great (died 604) was depicted in artwork wearing such a cap. The first usage of the actual word tiara is found in the life of Pope Paschal II (1099-1118) in the Liber Pontificalis. Around the mid-1200s, the ornamented circlet on the tiara became a highly decorated, tooth-edged crown. Pope Boniface VIII (1294-1303), who re-exerted papal authority over the secular monarchs, added a second crown, signifying his spiritual and temporal jurisdiction. Then, sometime before the death of Pope Benedict XII (1334-1342), a third crown was added, making it the triregno.
Three rationales justify the triregno: First, the crowns represent the Pope’s universal office, his jurisdiction over the whole church, and his temporal power. Second, they represent the pope’s authority over the church militant on earth, the church penitent in purgatory, and the church triumphant in heaven. Finally, the dominant rationale today, they represent that the ope is the Vicar of Christ, who shares in His three-fold office of priest, prophet, and king and consequently shares in His work to sanctify, teach and lead others in the faith.
Pope Paul VI, the last pope to use a papal tiara, updated the regulations for the election of a new Pope in “Romano Pontifici Eligendo” (1975), which specified a “coronation”: “Finally, the new pontiff is to be crowned by the senior cardinal deacon (No. 92). However, Pope John Paul I (1978) declined the use of a tiara as have his successors, Pope John Paul II (1978-2005) and Pope Benedict. Instead, at their “solemn inauguration” as Pope, the pallium was placed over their shoulders as a sign of fidelity to Christ. In 1996, when Pope John Paul II again updated the regulations, he deleted any reference to a coronation (“Universi Dominici Gregis,” No. 92). While the papal tiara has not been formally suppressed, perhaps its time has passed. Nevertheless, the new pope may choose the wear the tiara.