bull [Lat. bulla = leaden seal], papal letter. As the diplomatic organization of the papal chancery progressed in the Middle Ages, the papal bull came to be more solemn than the papal brief or encyclical. The letter, traditionally sealed with lead, but in special circumstances with silver or gold, begins with the name of the pope and his title as servus servorum Dei [servant of the servants of God]. Today only the consistorial bull, the most solemn of all papal pronouncements, carries the leaden seal; all other bulls and lesser documents have a red ink seal. The titles of bulls are the first few words of its Latin text. Famous bulls include Clericis laicos (1296) and Unam sanctam (1302) issued by Boniface VIII in his struggle with Philip IV of France; the Bull of Demarcation (1493) by Alexander VI; Exsurge Domine (1520) by Leo X against Martin Luther; Unigenitus (1713) by Clement XI, against Jansenism; Dominus ac Redemptor (1773) by Clement XIV, suppressing the Jesuits; Quanta cura (1864) by Pius IX, introducing the Syllabus errorum; Pastor aeternus (1871) by Pius IX, on papal infallibility; and Munificentissimus Deus (1950) by Pius XII, defining the dogma of the Assumption of the Virgin Mary. Pope John XXIII issued a consistorial bull, Humanae Salutis, in 1961 to convoke the 21st ecumenical council. The papal bull is used to proclaim the canonization of a saint. A bullarium is a collection of papal bulls; the most famous published bullaria are the Roman Bullarium (1733–62) and the Turin Bullarium (1857–85).