Assyrian administrative letters were written predominantly on clay tablets of standardized shape called egirtu, which were enclosed in clay envelopes and sealed with the sender's seal.[[10]] For understandable reasons, very few letter envelopes have actually survived, but the available evidence indicates that sealing and enveloping was the standard practice, even in the case of seemingly unimportant messages.[[11]]
Royal letters were sealed with the official royal signet ring (unqu). In this case, one can be sure that every letter really was sealed, for the word unqu not only means "signet ring" but is also the most frequent designation for royal letters in the present correspondence.
The purpose of enveloping naturally was to protect the contents of the letter from unwanted eyes. The seal functioned both as a certificate of the authenticity of the message and as a deterrent against clandestine breaking of the envelope. If any doubt as to the authenticity of the seal existed, the sender was immediately notified, as indicated by the following passage in a letter to Sargon:
"The 'seal' which he brought was not made like the seals of the king, my lord. There are 1,000 seal(-impression)s of the king my lord in my possession; I compared it with them, and it was not like the king my lord's seal. I am (herewith) returning the 'seal' to the king, my lord; if it really is the king my lord's seal, let them send [...] to me, and let me (then) place it with him and he may go where the king my lord sent him to." (CT 53 904).
10 egirtu was the most common designation of letters in Neo-Assyrian, but it can also mean"document" and actually refers to any one-column clay tablet showing a 1 : 2 ratio between the horizontal and vertical axis. Letters could also be called ṭuppu "tablet" (cf. no. 220) or nibzu (cf. ABL 798), a loan word from Aramaic identical in meaning with egirtu.
11 See, e.g., ABL 383. The envelope of this letter (containing a petition) was preserved obviously because the addressee never cared to read it.
Simo Parpola
Simo Parpola, 'Tablets, Envelopes, and Sealing', The Correspondence of Sargon II, Part I: Letters from Assyria and the West, SAA 1. Original publication: Helsinki, Helsinki University Press, 1987; online contents: SAAo/SAA01 Project, a sub-project of MOCCI, 2020 [http://oracc.org/saao/saa01/administrativecommunication/tabletsenvelopesandsealing/]