The 100 B.C. murals at San Bartolo, one 30 feet long, were found in a pyramid chamber below 50 feet of rubble. Dr. Saturno found the first painting when he ducked into a trench for shade and saw the face of a maize god on the north wall. It took two years of careful digging to expose the entire chamber.

Crazy!

On Ancient Walls, a New Maya Epoch - New York Times