It is important to bear in mind that, despite the importance of the Old Kingdom, the quality of the sources does not permit the writing of a consecutive political, military, and social history which could provide a full context for the rich achievement of the Old Kingdom in civilization and monumental architecture. ‘‘Factual’’ history, therefore, amounts of necessity to a gap-ridden framework of royal names, reign-lengths, genealogies, and information on royal achievements amounting, in essence, to pyramid and temple construction sites, gifts to the same temples (offerings, land, personnel), and military campaigns or economic expeditions (Baines 1995b: 129-30; Strudwick 2005). We should always remember that such data are not evenly spread from reign to reign, and that they have been far from easy to establish. The list and the order of monarchs still contains uncertainties even in the Third Dynasty, a period which also leaves us in the dark with regard to the reign-lengths: the life span of Djoser, for example, remains unknown, and the duration of the dynasty itself is uncertain. For the remainder of the Old Kingdom, although the chronological sources are more numerous, even the system of dating employed by the monarchy, that of the cattle counts, is problematic: it is of uncertain periodicity (in theory biennial, but this is doubtful for some reigns) and does not evolve into an annual accounting system until the Eighth Dynasty, a situation which makes it impossible to establish the exact reign lengths of kings (Hornung, Krauss & Warburton 2006: 116-58, contributions by Seidlmayer, Baud, and Verner). Whether a ruler was ephemeral or of long duration is decided by modern scholars on the basis of often faulty traditional sources (the Turin Royal Canon from the New Kingdom and the excerptors of Manetho), census dates of the Old Kingdom provided by the chance conservation of documents, the number of known monuments of a king, the number of references to him in private tombs, the royal cartouches which form part of personal names (‘‘Snefru is good’’), mortuary installations (‘‘The Mound ofNiuserre’’) or titles (‘‘Chief of Priests of the Pyramid of Pepi’’). All this means that, since relative dates (reign lengths), and absolute chronology (‘‘Before Christ’’) supplied in survey works only give a very rough idea, any lengthy elaborations based on them are by definition doomed to failure, though this should not forestall debate amongst Egyptologists who are aware of the problem. As far as we know, the five kings of the Third Dynasty covered barely more than 50 years; the Fourth Dynasty consisted of seven kings from Snefru to Shepseskaf (omitting, for lack of sources, the Thamphthis traditionally reputed to end the dynasty), with a duration of a century, and three long reigns of 25 years and more stand out, those of Snefru, Khufu, and Khafre; the Fifth Dynasty lasted about 130 years and had nine sovereigns from Userkaf to Unis many of whom reigned for less than 10 years, and some are very elusive (Neferefre, Shepseskare), while Niuserre (20?) and Djedkare (40?) enjoyed reigns of some length. Finally, the Sixth Dynasty consisted of six kings running from Teti to Merenre II; its long duration of nearly a century and a half is explained by the longevity of two of them: Pepi I (probably 50 years) and Pepi II (probably 60 years), against which the short reigns of two others, Userkare and Merenre II, stand in sharp contrast.