The oldest known pyramid in Egypt was built around 2630 B.C. at Saqqara, for the third dynasty's King Djoser. Known as the Step Pyramid. The pyramid’s architect was Imhotep, a priest and healer who some 1,400 years later would be deified as the patron saint of scribes and physicians. Over the course of Djoser’s nearly 20-year reign, pyramid builders assembled six stepped layers of stone, it was the tallest building of its time. The transition from the Step Pyramid to a true, smooth-sided pyramid took placed during the reign of King Snefru, founder of the Fourth Dynasty (2680–2560 BCE).