Bullae are mud/clay (or sometimes lead or tin) seals used to seal documents. In the ancient world, these seals were used in governmental, legal, or administrative contexts as a form of authentication and for tamper-proofing the information attached to the document.
Excavations in Jerusalem over the years have yielded quite a few bullae which contain the names of several kings, court officials and even one that refers to the name Isaiah, who is called nvy – “the prophet.”
In addition to other archaeological discoveries, these bullae provide additional evidence for the reliability of the historical narrative described and recorded on the pages of the Old Testament.