The Bent Pyramid is an ancient Egyptian pyramid located at the royal necropolis of Dahshur, approximately 40 kilometres (25 mi) south of Cairo, built under the Old Kingdom King Sneferu. A unique example of early pyramid development in Egypt, this was the second of four pyramids built by Sneferu.

The Bent Pyramid rises from the desert at a 54-degree inclination, but the top section (above 47 metres [154 ft]) is built at the shallower angle of 43 degrees, lending the pyramid a visibly “bent” appearance.

Archaeologists now believe that the Bent Pyramid represents a change from the step-sided pyramids of before to a smooth-sided pyramids. It has been suggested that due to the steepness of the original angle of inclination the structure may have begun to show signs of instability during construction, forcing the builders to adopt a shallower angle to avert the structure’s collapse. This theory appears to be born out by the fact that the adjacent Red Pyramid, was built immediately afterwards by Sneferu, constructed at an angle of 43 degrees from its base. This fact also contradicts the theory that at the initial angle the construction would take too long because Sneferu’s death was nearing, so the builders changed the angle to complete the construction in time. In 1974, Kurt Mendelssohn suggested the change of the angle to have been made as a stability precaution in reaction to a catastrophic collapse of the Meidum Pyramid while it was still under construction.

The reason why Sneferu abandoned the Meidum Pyramid and its Step Pyramid may have been a change in ideology. The royal tomb was no longer considered as a staircase to the stars; instead, it was served as a symbol of the solar cult and of the primeval mound from which all life sprang. It is also unique among the approximately one hundred and eighteen pyramids to be found in Egypt, in that its original polished limestone outer casing remains largely intact. British structural engineer Peter James attributes this to larger clearances between the parts of the casing than used in later pyramids; these imperfections would work as expansion joints and prevent the successive destruction of the outer casing by thermal expansion.

The ancient formal name of the Bent Pyramid is generally translated as (The)-Southern-Shining-Pyramid, or Sneferu-(is)-Shining-in-the-South. In July 2019, Egypt decided to open the Bent Pyramid for tourism for the first time since 1965. Tourists are able to reach two 4,600-year-old chambers through a 79-metre (259 ft) narrow tunnel built from the northern entrance of the pyramid. The 18-metre-high (59 ft) “side pyramid”, which is ᴀssumed to have been built for Sneferu’s wife Hetepheres will also be accessible. It is the first time this adjacent pyramid has been opened to the public since its excavation in 1956.

The Pyramid underwent three construction phases. In the first construction phase, a steep pyramid with a base length of 157 meters and an inclination angle of approximately 58° (possibly even 60°) was planned. If the pyramid had been completed in this form, it would have reached a height of around 125 meters, but given the knowledge of ancient techniques and the comparison with completed pyramids, such a steep pyramid was probably not a realistic option and did not exceed only few stone layers. Due to the good overall degree of preservation of the pyramid, this phase can only be proven indirectly through offset points around 12.70 m from the entrance in the lower descending corridor and at around 11.60 meters in the upper descending corridor. In the second phase, the builders reduced the angle of inclination to 54°. This increased the base length to 188 m. Here, too, inclined wall layers were used as in the step pyramids, because masons were not able to produce trapezoid stones at this phase. While step pyramids were built in ring-shaped shells of slant layers, the turn to undivided masonry made horizontal layers more practicable. If the inclination of 54° had been maintained, it would have reached a height of 129.4 m and a volume of around 1,524,000 cubic meters. The Bent Pyramid would therefore be the third highest pyramid in the world. However, this inclination was not continued beyond a height of 49 m. The masonry of this phase is faced with fine Tura limestone. In the third construction phase, the angle was reduced to 43° and, like in the Red Pyramid and all successive pyramids, the masonry was laid in horizontal layers. The slope reduction created the unique kink that is not found in any other pyramid. Due to the lower inclination angle of the upper part, the total height was reduced to 105 m. The total volume was 1,440,808 cubic meters. The upper area also has a cladding of fine Tura limestone.

Recent conclusions rather speak against a connection between the change in slope and structural defects. It is rather doubtful that a reduction in weight was a relevant criterion for a structure of almost closed mᴀss. The early decision against the 60° inclination initially envisaged rather suggests that geometric aspects were the decisive factor in the gradient change. Following the ᴀssumption of tangential construction ramps inclined up to 10° as the simplest form of ramp, the fact edge lengths became smaller as the height increased made it increasingly difficult to keep the gradient low. This could be compensated for by reducing the ramp width to around 3 m, which was sufficient for pairs of train crews, but even for such narrow ramps the geometric volume could not provide enough space when the gradient was too steep. Models and abstract calculations were not possible in that time. It must therefore have become clear to the construction managers halfway up that ramp structures would not be feasible when maintaining this gradient. In fact, all completed pyramids (first the Red, then the Great Pyramid) never exceeded the maximum gradient of 53°.

The Bent Pyramid has two entrances, one fairly low down on the north side, to which a substantial wooden stairway has been built for the convenience of tourists. The second entrance is high on the west face of the pyramid. Each entrance leads to a chamber with a high, corbelled roof; the northern entrance leads to a chamber that is below ground level, the western to a chamber built in the body of the pyramid itself. A hole in the roof of the northern chamber (accessed today by a high and rickety ladder 15 m (50 ft) long) leads via a rough connecting pᴀssage to the pᴀssage from the western entrance.

The western entrance pᴀssage is blocked by two stone blocks which were not lowered vertically, as in other pyramids, but slid down 45° ramps to block the pᴀssage. One of these was lowered in antiquity and a hole has been cut through it, the other remains propped up by a piece of ancient cedar wood. The connecting pᴀssage referenced above enters the pᴀssage between the two portcullises.

A particular feature in the chambers are a row of original cedar beams that were interpreted by many as a reaction on structural problems. In contradiction to that, Edwards argues the cedar beams rather had been part of the funerary support structure and, some of them bedded in mortar, could not have any structural function.