Sitting just a few miles outside the city of Puebla in central Mexico is the largest monument ever constructed on earth, but one would be hard-pressed to find it.
Covered in a rash of grass, trees and soil, and laying in the shadow of the Popocatepétl volcano is the Great Pyramid of Cholula, which at 1,500 feet wide and more than 200 feet tall is four times larger than the Great Pyramid at Giza and nearly twice the volume.
But for over a millennia the pyramid – known locally as Tlachihualtepetl or "man-made mountain” – lay hidden in plain sight as a thick layer of jungle foliage had already engulfed the structure by the time Hernán Cortés and his Spanish Conquistadores began their conquest of Mexico in the 16th century.
When Cortés arrived at the city of Cholula, the Spanish leader met little resistance from an indigenous people who invested more time in building temples to their gods than weapons to fend off enemies and during a three hour period on October 19, 1519 the Spanish slaughtered around 3,000 people, ransacked the city of its treasures and set ablaze the pyramids.
All except the Great Pyramid of Cholula, which the Spanish took to be a massive hill and where they chose to erect the Iglesia de Nuestra Señora de los Remediosa. That church also holds the title of the oldest continuously occupied building on the continent.
It wasn’t until 1910 when locals began to construct an insane asylum and realized that they were working on ground that wasn’t just a grassy hill.
While early excavations revealed numerous skeletons and even the deformed skulls of decapitated children, there is still very little known about the Pyramid of Cholula.
It is believed to have been constructed around 300 B.C. and the people who inhabited the city surrounding the pyramid – which at its height was the second-largest city in the Aztec Empire – are believed to have been a cosmopolitan, moneyed class who made their fortunes on the various trade routes that weaved through the area.
“It appears to have been multi-ethnic, with a great deal of migration,” David Carballo, an archaeologist at Boston University, told the BBC.
The pyramid is constructed similarly to a Russian doll with six different layers. Researchers believe that successive generations built and improved on what had already been constructed.
“They made a conscious effort to maintain and in some cases display previous construction episodes. This is pretty novel, and shows deliberate efforts to link to the past,” Carballo said.
The pyramid was constructed out of adobe bricks and at the height of Choluteca power was painted red, black and yellow insects. The pyramid, however, was abandoned sometime during the 7th or 8th century and the adobe bricks made fertile soil for vegetation to grow on top of.
By the time Cortés arrived it was already well hidden, leaving the conquistadores newer structures to destroy and remaining a mystery for centuries to come.