14 June 2016 And so scientists have had to piece together clues as to how these towering monuments were constructed. Over the past two decades, a series of new discoveries and studies allowed researchers to paint a clearer picture of those feats. [In Photos: Inside Egypt's Great Pyramids] Giza pyramids The first, and largest, pyramid at Giza was built by the pharaoh Khufu (reign started around 2551 B.C.). His pyramid, which today stands 455 feet (138 meters) tall, is known as the "Great Pyramid" and was considered to be a wonder of the world by ancient writers. The pyramid of Khafre (reign started around 2520 B.C.) was only slightly smaller than Khufu's but stood on higher ground. Many scholars believe that the Sphinx monument, which lies near Khafre's pyramid, was built by Khafre, and that the face of the Sphinx was modeled after him. The third pharaoh to build a pyramid at Giza was Menkaure (reign started around 2490 B.C.), who opted for a smaller pyramid that stood 215 feet (65 m) high.