By Miguel Angel Gutierrez

MEXICO CITY (Reuters) – Archeologists are opening a cave sealed for more than 30 years deep beneath a Mexican pyramid to look for clues about the mysterious collapse of one of ancient civilization’s largest cities.

The soaring Teotihuacan stone pyramids, now a major tourist site about an hour outside Mexico City, were discovered by the ancient Aztecs around 1500 AD, not long before the arrival of Spanish explorers to Mexico.

But little is known about the civilization that built the immense city, with its ceremonial architecture and geometric temples, and then torched and abandoned it around 700 AD.

Archeologists are now revisiting a cave system that is buried 20 feet beneath the towering Pyramid of the Sun and extends into a tunnel stretching for some 295 feet (90 meters) with a height of 8 feet.

They say new excavations begun this month could be the key to unlocking information about the sacred rituals of the people who inhabited the city, later dubbed “The Place Where Men Become Gods” by the Aztecs who believed it was a divine site..