Using seals can be traced back to ancient Mesopotamia when clay was
pressed with engraved cylinders to authenticate the tablets. The use of
wax seals began in the Middle Ages, and was originally reserved for the
wealthy or ruling classes. They were used for issuing official decrees and
legitimizing and authenticating official documents. The use became more
widespread and by the 13th century were used in monasteries, guilds, and
by common people. Seals were a good way to leave a signature in a time
when illiteracy was widespread, and could contain an initial or just a
small picture. These seals were usually in the form of a signet ring, and
instances of signet rings dates back to ancient Egypt. Signet rings were
unique to their wearer, and there are stories of visitors having to kiss
the signet ring of powerful aristocrats or church leaders. The signet ring
was a way to prevent forgeries or unauthorized documents, and were
destroyed when the owner died. Most of these early uses were not to seal
an envelope, the most common way wax seals are thought of, but to affix a
signature to a document.
Credit: FredLake