The name of the citadel that extends over the green valley and up through the clouds comes from the native words for “old” or “ancient” — Machu, and “peak” or “mountain — Picchu. Old Mountain is a proper name for a structure whose rocks date back to 250 – 450 million years ago. It was built around the the 1500s, according to experts, yet less is known about it than of the great pyramids of Egypt constructed much earlier. As befits such a mysterious structure, its entire discovery was a result of a happy accident.

On this day, July 24, in 1911, Yale University professor and explorer Hiram Bingham was on a trail high up in the Peruvian Andes when a hike led by one of the natives led him to the towering Machu Picchu.

Bingham brought his momentous discovery to light via an article in the National Geographic magazine. He was certain he had discovered the fabled lost city Vilcabamba, the Incan Empire’s last stand against the Spanish. That lost city was found later, but the location of Machu Picchu presented a mystery no less enticing: another lost city, with a monumental structure, that was abandoned in the face of an incoming Spanish invasion just 100 years after its completion. Who built the structure, how, and for what reasons may be questions with answers lost to history.