Bulla (seal)

A bulla (Medieval Latin for "a round seal", from Classical Latin bulla, "bubble, blob"; plural bullae) is an inscribed clay, soft metal (lead or tin), bitumen, or wax token used in commercial and legal documentation as a form of authentication and for tamper-proofing whatever is attached to it (or, in the historical form, contained in it).

In their oldest attested form, as used in the ancient Near East and the Middle East of the 8th millennium BC onwards, bullae were hollow clay balls that contained other smaller tokens that identified the quantity and types of goods being recorded. In this form, bullae represent one of the earliest forms of specialization in the ancient world, and likely required skill to create.^[1]: 24 From about the 4th millennium BC onwards, as communications on papyrus and parchment became widespread, bullae evolved into simpler tokens that were attached to the documents with cord, and impressed with a unique sign (i.e., a seal)^[1]: 29 to provide the same kind of authoritative identification and for tamper-proofing. Bullae are still occasionally attached to documents for these purposes (e.g., the seal on a papal bull).