The oldest of the Seven Wonders of the Ancient World and the only one that survives today, the Great Pyramid of Giza was constructed as a tomb for the Egyptian pharaoh Khufu. The precise details regarding the pyramid’s construction remain a mystery, as no written records have been found, but a number of estimates place its completion at sometime between 2560 B.C. and 2540 B.C.

The pyramid initially rose about 481 feet, making it the world’s tallest man-made structure for thousands of years until it was surpassed in the early 1300s by England’s Lincoln Cathedral. Due to erosion, the pyramid now stands around 455 feet tall.

Covering an area of 13 acres, the massive monument was designed to align with the points of the compass and built with an estimated 2.3 million stones, each weighing a ton or more on average. The workforce is thought to have consisted of thousands of skilled tradesmen and paid laborers, as opposed to slaves, and estimates suggest the project took about two decades to complete. It’s been speculated that workers created ramps in order to move the stone building blocks into place on the pyramid.

In addition to Khufu’s pyramid, two other large pyramids for pharaohs were erected at the Giza site, one for his son Khafra (it originally stood 471 feet high) and the other for Khafra’s son Menkaure (originally 218 feet high). Khafra’s pyramid complex is home to the famous Great Sphinx statue, which measures 241 feet long and about 66 feet high. Over the ages, all three pyramids have been targeted by grave robbers and much of their exterior white limestone stolen, possibly for use in other building projects.