— A papal bull is an official document issued by the pope which is traditionally affixed with a lead seal known as the "bulla."
— Since the 12th century, the seal carries the heads of apostles Peter and Paul on one side and the pope's signature on the other.
— The bulls have been used for centuries to call crusades, excommunicate perceived heretics such as Martin Luther, canonize saints and even admonish specific adulterers.
— The Papal Bulls of Discovery in 1455 and 1493 gave Catholic explorers "full and free power, authority, and jurisdiction of every kind" in land that was not occupied by Christians. They also outlined their "duty to lead the peoples dwelling in those islands and countries to embrace the Christian religion."
— Bulls have been used less frequently since the appearance of papal briefs, a less formal method of communication. Most papal letters are now issued as briefs.