TEOTIHUACAN, Mexico

The key to understanding one of this country’s most mysterious sites may be all in the water.

The ancient city of Teotihuacan, which includes some of the world’s biggest pyramids, collapsed 1,400 years ago. Ever since then, the site in central Mexico has confounded scholars.

Verónica Ortega, of Mexico’s National Institute of Anthropology and History, says her excavations in recent months at Teotihuacan’s square of the Pyramid of the Moon have yielded a breakthrough, suggesting the whole city was an aquatic sanctuary consecrated to the worship of water. The 43-year-old archaeologist has found canals and cavities similar to pools beneath the square, along with sculptures of water gods. Excavations at Teotihuacan’s other two pyramids uncovered seashells, water pitchers and more aquatic elements.

“Water is the true protagonist of Teotihuacan. If there was a city in the ancient world where water was worshipped, it was Teotihuacan,” Ms. Ortega said on a recent morning in her office at the excavation site, which looks out on one of Teotihuacan’s three pyramids.