What Is: a Papal Bull

In the Medieval world, there were two sources of authority, the secular under the King, Duke or other local lord, and the religious, in the form of the Church.  In many ways, the authority of the Church was more important.  While Kings and other overlords had control of the daily lives of their subjects, the Church controlled everyone's immortal soul.  Thus, when a Pope or his representatives, such as bishops or cardinals, spoke on matters of law, morals, or even political concerns, it carried a lot of weight.  The Pope issued his pronouncements in the form of a written document known as a Papal bull.

The word bull comes from the Latin bulla, and refers to a seal attached to a document.  Bullae served as a means of authenticating a document and tamper-proofing it, since the twine attaching the leaden seal was threaded through the bottom of the document itself.  A Papal Bull could deal with any subject, from pronouncements of Church doctrine, canonization of saints, excommunications and interdicts, appointment of bishops, or even the settling of disputes.  A bull usually began with a few key words, known as an incipit, which served as the title of the bull.  The seal showed Saints Peter and Paul on one side, one the other was the name of the Pope issuing the bull.  The cord attaching the lead seal to the document could be of hemp or, in certain cases, of silk.  Likewise, though the most common material for the seal was lead, it could in rare cases be cast of gold.  Incidentally, Popes weren't the only issuers of bulls.  Decrees of Byzantine emperors were also sealed in the same way, and called bulls, as were the decrees of some Holy Roman Emperors.