The CKU letters are known only through copies written on clay tablets as school exercises by students learning to write cuneiform.
All but one of the known copies have been dated to the Old Babylonian period, and were found in cities of Mesopotamia or the broader Near East, including Nippur, Ur, Isin, Uruk, Kish, Sippar, and Susa.
A single tablet bearing copies of two of the letters and dating to the Middle Babylonian period was also found at Susa.
[3] They loosely conform to the following structure:[4] Most of the letters are presented as an exchange between a king of the Ur III dynasty and one of his officials (some of whom are known historical figures, e.g., the general Aradmu and later king of Isin Išbi-Erra), usually discussing matters of state or administration.
Ibbi-Sin to Puzur-Numušda 1 The historical authenticity of the Correspondence of the Kings of Ur – the question of whether they originally date, as they purport, to the Ur III period, or whether they were composed during Old Babylonian compositions – is a highly contested and complicated issue.
[5] For many years, the letters were treated as one of the best sources of information for reconstructing political events of the Ur III period, especially the end of the kingdom.
The modernistic account of the end of the Ur III dynasty, for example (catastrophic collapse due to factors such as Amorite invasions, environmental disasters and crop failures, and the rise of bloated bureaucracy), is largely based on CKU.
[6] However, the historicity of the letters has recently been called into question, sparking at times intense debate among scholars.
[10] Piotr Michalowski, in his 2011 publication of the entire CKU, presented an argument against both viewpoints.