Archaeologists found around 50,000 objects in a tunnel inside the Temple of the Feathered Snake in Teotihuacán, an enigmatic city that flourished between the second and the fifth century of our era 50 kilometers (31 miles) northeast of Mexico City.

Objects such as batons, offerings, seeds, animal skeletons that could be jaguars and metal spheres have been found in a 150-meter-long tunnel (492 feet) inside the Quetzalcóatl Pyramid, the third largest in the archaeological site.

The Tlalocan project (which means 'I walk under the Earth' in Náhuatl), started five years ago and was funded by the National Institute of Anthropology and History of Mexico (INAH). 

"It's amazing," said Sergio Gómez, the Mexican archeologist in charge of the excavation at the "City of the Gods", the first major Mesoamerican metropolis. 

The temperature drops as you descend and moisture increases. Wooden boards preserve the muddy tunnel floor. "They wanted to recreate the outside world, so they excavated until they hit the phreatic zone in order to have rivers," Gómez explained. 

Near the entrance, a sort of chimney connects to the outside, perhaps an observatory, says the archaeologist about the structure, that sank by accident in 2003 and helped Gómez and French archaeologist Julie Gazzola find the tunnel.

The ceiling of the tunnel, which remained untouched for 1,800 years, is "painted" with metal powder, pyrite or magnetite, that was probably brought from another place because the material is not available in the area. 

Over 300 spheres, with a diameter from 2 to 25 centimeters (0.7 to 9.8 inches), were found inside two chambers. 

"We still do not know what they symbolize. The sea? Raindrops?" Gómez wondered. 

At a press conference, Gómez said that rubber balls, sculptures, jade and wooden pieces, ceramic objects, seashells and marine elements from the Gulf of Mexico and the Caribbean Sea were also found inside the pyramid.