Bent Pyramid of Dahshur: Sneferu's Changing-Angle Pyramid

The Bent Pyramid of Dahshur is a royal pyramid built for the pharaoh Sneferu around 2600 BC, about 40 kilometres south of modern Cairo. Its sides rise steeply and then, about halfway up, abruptly change to a gentler slope. This unusual profile makes it one of the clearest records of how Egyptian builders learned, by trial and error, to make a true smooth-sided pyramid.

Background: Sneferu and the search for the true pyramid

Before Sneferu, the largest royal tomb in Egypt was the Step Pyramid of Djoser at Saqqara, a stack of six stone platforms. Sneferu, founder of the Fourth Dynasty, wanted something new: a geometric pyramid with straight, smooth sides. The length of his reign is debated, with estimates ranging from about 24 to more than 40 years.

He is linked to three large pyramids. The pyramid at Meidum was probably begun as a step pyramid and later converted. The Bent Pyramid was his first attempt to build a true pyramid from the start. His third, the Red Pyramid, stands about two kilometres to the north and finally succeeded.

Why the angle changes

The lower part of the Bent Pyramid rises at roughly 54 degrees. At a height of about 47 metres the slope drops to roughly 43 degrees. Studies of the structure suggest that the original plan may have been even steeper, and that a belt of extra masonry was added around the base early on to reduce the angle to 54 degrees.

The usual explanation is structural. The pyramid stands on clay and soft rock, and its inner chambers show cracks and signs of settling that the ancient builders tried to repair, including with wooden beams of cedar. A steep pyramid puts enormous weight on its core. By lowering the angle, the builders cut the volume and weight of the upper half.

Other theories have been proposed, such as a rush to finish the tomb because the king was ill. These have little support. The engineering explanation fits the evidence better, and the next pyramid, the Red Pyramid, was built at the gentler 43-degree slope from the ground up.

Inside the pyramid

The Bent Pyramid is unusual in having two entrances. One is on the north face, as was normal, and the other is high on the west face. Each leads through its own passage to a separate chamber with a tall corbelled roof, a ceiling made of stone courses that step inward as they rise.

The two systems are joined by a rough passage that appears to have been cut later. Why the builders planned two separate chamber systems is not certain. It may reflect religious ideas about the king’s journey after death, or changes of plan during construction.

The surviving casing

The pyramid’s most striking feature today is its outer casing of fine white limestone. Most Egyptian pyramids lost their casing to stone robbers in the medieval period, leaving only the rougher core. At the Bent Pyramid large areas of smooth casing still cover the faces.

The casing blocks were laid sloping inward, which helped hold them in place. Dahshur was also a long way from medieval Cairo’s building sites. For this reason the Bent Pyramid gives modern visitors the best idea of how a newly finished pyramid looked.

The wider complex

Like later royal pyramids, the Bent Pyramid was part of a complex. A small satellite pyramid stands to the south, and a modest offering chapel lay against the east face. A causeway ran down to a valley temple, which was excavated in the 1950s by the Egyptian archaeologist Ahmed Fakhry and contained finely carved reliefs and statues.

The British engineer John Shae Perring explored the interior in 1839, and later teams have continued to study the site. Dahshur lay inside a military zone for much of the 20th century and only opened to tourism in the 1990s. In 2019 Egypt opened the interior of the Bent Pyramid and its satellite pyramid to the public.

By the numbers

Timeline

• c. 2600 BC: Sneferu’s builders begin the pyramid at Dahshur as a steep true pyramid.
• c. 2600 BC: The slope is reduced in the upper half, and work starts on the Red Pyramid nearby.
• 1839: John Shae Perring explores and records the interior.
• 1951–1955: Ahmed Fakhry excavates the valley temple and its reliefs.
• 1979: Dahshur is included in the UNESCO World Heritage site of Memphis and its Necropolis.
• 2019: The interior opens to visitors after restoration.

Why it matters

The Bent Pyramid is a monument to a mistake that was corrected in stone. It shows the builders of the Old Kingdom testing the limits of their materials, and the lessons they learned there made possible the Red Pyramid and, a generation later, the Great Pyramid of Giza.