Forming the backbone of Egyptian chronology are the regnal years as recorded in Ancient Egyptian king lists. Surviving king lists are either comprehensive but have significant gaps in their text (for example, the Turin King List), or are textually complete but fail to provide a complete list of rulers (for example, the Abydos King List), even for a short period of Egyptian history. The situation is further complicated by occasional conflicting information on the same regnal period from different versions of the same text; thus, the Egyptian historian Manetho's history of Egypt is only known by extensive references to it made by subsequent writers, such as Eusebius and Sextus Julius Africanus, and the dates for the same pharaoh often vary substantially depending on the intermediate source.