Other Egyptologists suspect a reign of less than 30 years for Unas, owing to the scarcity of artefacts datable to his reign as well as the lack of documents dated to beyond his eighth year on the throne. Hence, Jürgen von Beckerath believes that Unas ruled Egypt for 20 years while Rolf Krauss, David Warburton and Erik Hornung shortened this number to 15 years in their 2012 study of Egyptian chronology. Krauss and Miroslav Verner further question the credibility of the Turin Canon concerning the Fourth and Fifth Dynasties, so that the 30-year figure credited to Unas by the canon might not be reliable.