SIGNED, SEALED, DELIVERED. In antiquity, seals were small carved stones or gems used as instruments of identification, authority and security. When sending a letter, an official would roll or fold up the document and tie it with string. He then placed a wet blob of clay over the knot and pressed his seal into it, thus marking it with his official signature and ensuring the security of the contents until the letter reached the intended recipient.
We have numerous examples of seals and bullae from antiquity. In most cases they are no longer with the documents they protected; often these were destroyed in fires that burnt away the papyrus and string but baked and thereby preserved the bullae (the string marks are visible on the back of this bulla).