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]
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.
Planning the pyramids
The pharaohs appointed a high-ranking official to oversee pyramid construction. In 2010, a team of archaeologists discovered papyri dating to the reign of Khufu at the site of Wadi al-Jarf on the Red Sea. Text on the papyri stated that in the 27th year of Khufu's reign, the pharaoh's half-brother, Ankhaf, was the vizier (highest official to serve the king in ancient Egypt) and "chief for all the works of the king," archaeologists Pierre Tallet and Gregory Marouard wrote in the journal Near Eastern Archaeology.
While the papyri said that Ankhaf was in charge during the pharaoh's 27th year, many scholars believe it's possible that another person, possibly the vizier Hemiunu, was in charge of pyramid building during the earlier part of Khufu's reign.
Researchers are working to understand the sophisticated planning that would have been involved in pyramid building, which required constructing not just the pyramids, but also the temples, boat pits and cemeteries located near the enormous structures.
Researchers have noted that the Egyptians had the ability to align structures to true north very precisely, something that may have helped in planning the pyramids. Glen Dash, an engineer who studies the pyramids at Giza as part of Ancient Egypt Research Associates (AERA), noted that Khufu's pyramid is aligned to true north within one-tenth of a degree. How the ancient Egyptians did this is not fully clear. In a report published recently in an AERA newsletter, Dash wrote that a circumpolar star like Polaris and lines of rope were likely used as part of the method.
Supplies and food
Over the past few years archaeologists with AERA have been excavating and studying a port at Giza that would have been used to bring in supplies, food and people. The papyri found at Wadi al-Jarf allude to the importance of Giza's ports, saying that limestone blocks, used in the outer casing of the pyramid, were shipped from quarries to the pyramid sites within a few days using boat transport.
The port that AERA archaeologists found is located by a town built near Menkaure's pyramid. This town had sizable homes for high officials, a barracks complex that likely held troops and buildings where large numbers of clay seals (used in record keeping) were found. The ordinary workers likely slept in simple dwellings near the pyramid site.
Estimates given by various archaeologists for the size of the workforce at Giza tend to hover around 10,000 people for all three pyramids. These people were well-fed; in a study published in 2013, Richard Redding, the chief research officer at AERA, and colleagues found that enough cattle, sheep and goats were slaughtered every day to produce 4,000 pounds of meat, on average, to feed the pyramid builders. The finding was detailed in the book "Proceedings of the 10th Meeting of the ICAZ Working Group 'Archaeozoology of Southwest Asia and Adjacent Areas'" (Peeters Publishing, 2013). Redding used the animal bone remains found at Giza, and the nutritional requirements for a person doing hard labor, to make the discovery.
Redding also found that animals were brought in from sites on the Nile Delta and kept in a corral until they were slaughtered and fed to the workers.
The workers' meat-rich diet may have been an inducement for people to work on the pyramids, Redding said. "They probably got a much better diet than they got in their village," Redding told Live Science in 2013.
Quarrying the blocks
Many of the stones used in Khufu's pyramid are from a horseshoe-shaped quarry located just south of the pyramid, said Mark Lehner, an Egyptologist who leads AERA, and engineer David Goodman. They published their finds back in 1985 in the journal Mitteilungen des Deutschen Archäologischen Instituts.
Construction workers would have used blocks from a quarry located south-southeast of Menkaure's pyramid to build that pyramid, the researchers said. However, it is unclear which quarry was used for Khafre's pyramid.
When nearly complete, each of the Giza pyramids was furnished with a smooth outer casing made of limestone. Little of this outer casing remains today, having been reused for other building projects in Egypt over the millennia.
The papyri found at Wadi al-Jarf said that the limestone used in the casing is from a quarry located at Turah, near modern-day Cairo, and was shipped to Giza by boat along the Nile River and a series of canals. One boat trip took four days, the papyri said.
Moving the blocks
To move the stones overland, the Egyptians would have used large sledges that could be pushed or pulled by gangs of workers. The sand in front of the sledge was likely dampened with water, something that reduced friction, making it easier to move the sledge, a team of physicists from the University of Amsterdam found in a study published in 2014 in the journal Physical Review Letters.
"It turns out that wetting Egyptian desert sand can reduce the friction by quite a bit, which implies you need only half of the people to pull a sledge on wet sand, compared to dry sand," Daniel Bonn, a physics professor at the University of Amsterdam and lead author of that study, told Live Science in 2014. The scientists said scenes in ancient Egyptian artwork show water being poured in front of sledges.
Most Egyptologists agree that when the stones arrived at the pyramids, a system of ramps was used to haul the stones up. However, Egyptologists are uncertain how these ramps were designed. Little evidence of the ramps survives, but several hypothetical designs have been proposed over the last few decades.
New data may come from the Scan Pyramids Mission, an initiative being undertaken by researchers at three different universities, the Heritage Innovation Preservation Institute and the Egyptian Ministry of Antiquities. This project's scientists are in the process of scanning and reconstructing the Giza pyramids using a variety of technologies. In addition to finding out more about the construction of the pyramids, the project may also reveal if there are any undiscovered chambers within the structures.
Original article on Live Science.