The period of Ancient Egyptian history known as wehem mesut or, more commonly, Whm Mswt (Manuel de Codage transliteration: wHm msw.t) can be literally translated as Repetition of Births, but is usually referred to as the (Era of the) Renaissance.
The Whm Mswt forms part of the reign of Ramesses XI, a king who ruled around the end of the New Kingdom and the start of the Third Intermediate Period. In his 19th year he began to count anew, with year 1 of the Whm Mswt perhaps identical to, but at least partly overlapping with his 19th regnal year, as can be seen from the headings of two lists of thieves, known as the Abbott Dockets. These read:
-Year 1, first month of inundation, day 2, corresponding to Year 19
-Year 1, second month of inundation, day 24, corresponding to Year 19
For a long time it was unclear where the Whm Mswt should be placed chronologically. Since the reign of Ramesses IX lasted into its 19th year, the Abbott Dockets were sometimes taken as evidence that the era immediately followed his reign and might perhaps even have been identical to (a phase of) the reign of Ramesses X. This seemed to be confirmed by the fact that both the years 16 and 17 of Ramesses IX and the first two years of the Whm Mswt saw a series of court sessions connected with tomb-robbery. It was Jaroslav Černý who convincingly showed that the era started in year 19 of Ramesses XI. Although generally accepted, as a side effect his solution created an interval of over two decades between the two series of tomb-robbery trials, which created some anomalies for the tomb-robbery papyri.
It is often (tacitly) assumed that the start of the Whm Mswt coincided with the accession date of Ramses XI, but this is nothing more than a hypothesis. Whereas it now seems beyond doubt that the accession date of Ramses XI (= the date on which his regnal year changed) fell on "month 11, day 20", it does not automatically follow that the year change for the Renaissance coincided with this date as well. It is safer to recognize that we simply don't know the precise date on which the Whm Mswt was inaugurated.