The system of Manetho, in the state in which it has been handed down to us by epitomizers, has rendered, and continues to render, service to science; if it is not the actual history of Egypt, it is a sufficiently faithful substitute to warrant our not neglecting it when we wish to understand and reconstruct the sequence of events. His dynasties furnish the necessary framework for most of the events and revolutions, of which the monuments have preserved us a record. At the outset, the centre to which the affairs of the country gravitated was in the extreme north of the valley. The principality which extended from the entrance of the Fayum to the apex of the Delta, and subsequently the town of Memphis itself, imposed their sovereigns upon the remaining nomes, served as an emporium for commerce and national industries, and received homage and tribute from neighbouring peoples. About the time of the VIth dynasty this centre of gravity was displaced, and tended towards the interior; it was arrested for a short time at Heracleo-polis (IXth and Xth dynasties), and ended by fixing itself at Thebes (XIth dynasty). From henceforth Thebes became the capital, and furnished Egypt with her rulers. With the exception of the XIVth Xoite dynasty, all the families occupying the throne from the XIth to the XXth dynasty were Theban. When the barbarian shepherds invaded Africa from Asia, the Thebaid became the last refuge and bulwark of Egyptian nationality; its chiefs struggled for many centuries against the conquerors before they were able to deliver the rest of the valley. It was a Theban dynasty, the XVIIIth, which inaugurated the era of foreign conquest; but after the XIXth, a movement, the reverse of that which had taken place towards the end of the first period, brought back the centre of gravity, little by little, towards the north of the country. From the time of the XXIst dynasty, Thebes ceased to hold the position of capital: Tanis, Bubastis, Mendes, Sebennytos, and above all, Sais, disputed the supremacy with each other, and political life was concentrated in the maritime provinces. Those of the interior, ruined by Ethiopian and Assyrian invasions, lost their influence and gradually dwindled away. Thebes became impoverished and depopulated; it fell into ruins, and soon was nothing more than a resort for devotees or travellers. The history of Egypt is, therefore, divided into three periods, each corresponding to the suzerainty of a town or a principality:-- I.--Memphite Period, usually called the "Ancient Empire," from the Ist to the Xth dynasty: kings of Memphite origin ruled over the whole of Egypt during the greater part of this epoch. II.--Theban Period, from the XIth to the XXth dynasty. It is divided into two parts by the invasion of the Shepherds (XVIth dynasty): a. The first Theban Empire (Middle Empire), from the XIth to the XIVth dynasty. b. The new Theban Empire, from the XVIIth to the XXth dynasty.