Oldest true pyramid

The oldest surviving true (i.e., straight-sided) pyramid is the Red Pyramid (aka North Pyramid), which sits within the Dahshur necropolis alongside the River Nile, south of Cairo, Egypt, and was constructed c. 2575–2563 BCE during the reign of Fourth Dynasty Pharaoh Sneferu (aka Soris). It represents the first purpose-built transition from earlier stepped pyramids (which generally had a flat top) to the more classic design we associate with pyramids today, with smooth, sloping sides that meet to form a pointed apex.

The Red Pyramid is so named owing to the reddish hue of the limestone used to build its core structure. However, it would not have appeared this colour when first completed as it was originally covered in white Tura limestone; most of this outer layer was taken for use in other buildings, particularly in Cairo, in the Middle Ages, leaving the redder base stone exposed.

During his reign in Old Kingdom Egypt in the 26th century BCE, Sneferu is credited with ushering in a golden era of pyramid building. As well as the Red Pyramid, he instigated the construction of at least three others, including the Bent Pyramid, found on the same site at Dahshur. This one takes its name from its unique shape: partway through its creation the angle of incline of the pyramid’s sloping walls altered from 54° (at the base) to a more gentle 43° (at the top), most likely to mitigate structural stability issues.

The earliest pyramid attributed to Sneferu is the Meidum Pyramid (also known as the Collapsed Pyramid owing to its long-time state of disrepair since ancient times), located south of Memphis, Egypt, which dates to c. 2600 BCE. This was originally created as a seven-stepped pyramid, possibly by Sneferu's predecessor Huni, and was later converted to a true pyramid by adding a layer of stones to encase the former structure. Over the centuries, much of this added-on layer has crumbled away, exposing once again the original step pyramid within, and much of the overall structure has been reclaimed beneath the desert sands. Many credit Meidum as the first prototype true pyramid, while the Red Pyramid is the first true pyramid built that way from scratch and to have retained its straight-sided structure to this day.

Arguably the most famous true pyramids are those found at Giza in Egypt, home to the world's tallest pyramid: the Pyramid of Khufu, or Great Pyramid. When completed around 4,500 years ago, it stood 146.7 m (481 ft 3 in), but erosion and vandalism over time have reduced its height to 137.5 m (451 ft 1 in) high today.