From Wikipedia

Great Pharaohs

Twilight For The Fourth Dynasty

The Old Kingdom is the name commonly given to that period in the 3rd millennium BC when Egypt attained its first continuous peak of civilization in complexity and achievement – this was the first of three so-called "Kingdom" periods, which mark the high points of civilization in the lower Nile Valley (the others being Middle Kingdom and the New Kingdom).

The term itself was coined by nineteenth century historians and the distinction between the Old Kingdom and the Early Dynastic Period is not one which would have been recognized by Ancient Egyptians. Not only was the last king of the Early Dynastic Period related to the first two kings of the Old Kingdom, but the 'capital', the royal residence, remained at Ineb-Hedg, the Ancient Egyptian name for Memphis. The basic justification for a separation between the two periods is the revolutionary change in architecture accompanied by the effects on Egyptian society and economy of large-scale building projects. 

The Old Kingdom is most commonly regarded as spanning the period of time when Egypt was ruled by the Third Dynasty through to the Sixth Dynasty (2686 BC – 2134 BC). Many Egyptologists also include the Memphite Seventh and Eighth Dynasties in the Old Kingdom as a continuation of the administration centralized at Memphis. The Old Kingdom was followed by a period of disunity and relative cultural decline referred to by Egyptologists as the First Intermediate Period.

The royal capital of Egypt during the Old Kingdom was located at Memphis, where Djoser established his court. The Old Kingdom is perhaps best known, however, for the large number of pyramids, which were constructed at this time as pharaonic burial places. For this reason, the Old Kingdom is frequently referred to as "the Age of the Pyramids."