TEOTIHUACAN, Mexico - Archeologists are unearthing a 2,000-year-old tunnel outside bustling modern day Mexico City searching for clues to one of the region's most influential former civilizations.

Heavy rains at the site of Teotihuacan, some 40 kilometers from the capital, accidentally provided the first sign of the tunnel's existence in 2003, when the water made a tiny hole in the ground.

Six years later, a team financed by Mexico's National Institute of Anthropology and History started digging at the site, which is one of the most visited in Mexico.