The Old Kingdom was a peak of civilisation and achievement. This was the first of three so-called "Kingdom" periods which mark the high points of civilization in the Nile Valley. It began when Egypt was ruled by the Third Dynasty through the Sixth Dynasty (2686–2181 BC). Many Egyptologists also include the Memphite Seventh and Eighth Dynasties in the Old Kingdom. The Old Kingdom was followed by a period of disunity called the First Intermediate Period, or as the Egyptians called it, the "first illness."