No cameras were around thousands of years ago when the ancient Egyptians built the three pyramids of Giza, for each of three pharaohs Khufu, Khafre and Menkaure.
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.
Over the past two decades, researchers have made a number of discoveries related to the pyramids, including a town built near the pyramid of Menkaure, a study showing how water can make blocks easier to move and a papyrus found by the Red Sea. These have allowed researchers to gain a better understanding of how the Giza pyramids were built. The new finds add to older knowledge gained over the last two centuries.
Developing pyramid-building techniques
The techniques used to build the Giza pyramids were developed over a period of centuries, with all of the problems and setbacks that any modern-day scientist or engineer would face.
Pyramids originated from simple rectangular "mastaba" tombs that were being constructed in Egypt over 5,000 years ago, according to finds made by archaeologist Sir Flinders Petrie. A major advance occurred during the reign of the pharaoh Djoser (reign started around 2630 B.C). His mastaba tomb at Saqqara started off as a simple rectangular tomb before being developed into a six-layered step pyramid with underground tunnels and chambers.
Another leap in pyramid-building techniques came during the reign of the pharaoh Snefru (reign started around 2575 B.C.) who built at least three pyramids. Rather than constructing step pyramids, Snefru's architects developed methods to design smooth-faced, true pyramids.
It appears that Snefru's architects ran into trouble. One of the pyramids he constructed at the site of Dahshur is known today as the "bent pyramid" because the angle of the pyramid changes partway up, giving the structure a bent appearance. Scholars generally regard the bent angle as being the result of a design flaw.
Snefru's architects would correct the flaw; a second pyramid at Dahshur, known today as the "red pyramid" — so named after the color of its stones — has a constant angle, making it a true pyramid.
Snefru's son, Khufu, would use the lessons from his father and earlier predecessors to construct the "Great Pyramid," the largest pyramid in the world.