English (United Kingdom) 
Russian (Russia) Unfortunately, we know a few about this rite. For the first time, it is found on the Gudea Cylinder A (II 23); later, it was mentioned in cuneiform literature up to the Seleucid Period. Perhaps, it was one of holidays the most mentioned in administrative and economic texts of Mesopotamia of all eras of its ancient history. We do not know, however, a single literary monument dedicated to that holiday.
The Sumerian word eš3-eš3 (from which Akkadian eššešu came) means ‘sanctuaries’; i.e. there was a rite that took place in numerous sanctuaries. The only mentioning of the rite on the Gudea Cylinder is connected with organization of the celebrations in honour of Ningirsu, who listened to the prayers of the ruler and accepted his sacrifice in the temple of Bagara. Gudea happily thanked the god for his understanding. Unfortunately, we know nothing about the calendar dates and periods of the holiday in the epoch of Gudea.
In the texts of the III Dynasty of Ur, the ritual of eššešu falls on the first, seventh, and fifteenth days of each month. In the very end of that epoch, and in the early Old Babylonian Period, they added also the twenty fifth day of each month to those holidays. On those days, people brought rich animal sacrifices, beer, and wine to the gods and praised them. In the royal hymn praising the virtues of deified Šulgi, they speak about eššešu organized by Šulgi for Inanna. Inanna as an object of eššešu was mentioned in some economic texts of that epoch.
Since the Kassites Period, the holiday of eššešu was celebrated on the fourth, eighth, and seventeenth days of each month. It was associated with god Nabu and it was preceded with a celebration for his father, god Marduk. In the post-Assyrian Babylonian state the holiday of eššešu was noted only in the texts from Uruk, where it took eight days in each month.
Initially the holiday was dedicated, evidently, to the lunar god and to the change of the Moon phases during a week. The very concept of the week was not known in the Sumerian epoch, but even then observant royal astrologers began to count the seven-day cycles within the monthly ones, and, by the end of each cycle, they hold a festival for the sake of propitiating the patron gods of the lunar course (as well as the gods-rulers of a given day). In the epoch of developed Babylonian ideology, the festival days were associated, obviously, with Nabu and Marduk. In the Seleucid Uruk, the first eight days of each month were taken for that festival in order to makr the first week cycle.
Thus, we believe that the ritual and festival of eššešu, held in sanctuaries of a certain type, were originally associated with the establishment of a week cycle in the calendars of Ancient Mesopotamia, connecting them to the change of the Moon phases. Mentions of Inanna in the context of that holiday suggest that it was tied to observations of the cycles of the planet of Venus.
Literature:
- A praise poem of Šulgi (Šulgi A) https://etcsl.orinst.ox.ac.uk/cgi-bin/etcsl.cgi?text=t.2.4.2.01
- http://psd.museum.upenn.edu/nepsd-frame.html ešeš
- Chicago Assyrian Dictionary E, 371-373 https://oi.uchicago.edu/sites/oi.uchicago.edu/files/uploads/shared/docs/cad_e.pdf