A sacred tunnel discovered in the ancient Mexican city of Teotihuacan is filled with thousands of ritual objects and may lead to royal tombs, the lead Mexican archaeologist on the project said on Wednesday. The entrance to the 1,800-year-old tunnel was first discovered in 2003, and its contents came to light thanks to excavations by remote-control robots and then human researchers, archeologist Sergio Gomez told reporters. The site is located about 30 miles (50 km) northeast of Mexico City. The ruins have long been shrouded in mystery because its inhabitants did not leave behind written records. The artifacts found inside the tunnel, located below the Temple of the Plumed Serpent, include finely carved stone sculptures, jewelry and shells.