Mexico City, Mexico - A sacred tunnel discovered in the ancient Mexican city of Teotihuacan is filled with 50,000 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 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. An estimated 50,000 objects, 4,000 made of wood as well as scores of obsidian blades and arrow heads, provide clues into how the city's priests and rulers conceived the underworld.

Deep: This picture released by the National Institute of Anthropology and History, shows part of the tunnel and offerings found inside the 'Temple of the Feathered Serpent.'

"Due to the magnitude of the offerings that we've found, it can't be in any other place," said Gomez, who works for Mexico's national anthropology and history institute, referring to the possibility of finding royal tombs. "We've been able to confirm all of the hypotheses we've made from the very beginning," he added, saying ongoing excavations could yield more major discoveries next year.

One of Mexico's most-visited ancient sites, Teotihuacan is home to massive pyramids, temples, and elite residences including many adorned with colorful murals. The city reached its peak between 100 B.C. and 650 B.C. with a population as large as 200,000, growing rich from a wide-ranging trade in obsidian that in pre-Colombian times was used to make knives and other weapons.

The city had long been abandoned by the time the Aztecs came to power in the "Valley of Mexico" in the 14th century, yet it continued to play an important role as a destination for religious pilgrimages. In Nahuatl, the Aztec language still spoken in many parts of Mexico, Teotihuacan means "abode of the gods."

But nearly 2,500 years after the city was founded - and about 2,100 years after the Teotihuacan culture began to flourish there - very little is known about the identity of its rulers. No depiction of a ruler, or the tomb of a monarch, has ever been found, setting the metropolis apart from other pre-Hispanic cultures that deified their rulers.

Vertical excavations begun in 2009 to reach the mouth of the tunnel suggest it was a ruler's tomb, archaeologist Sergio Gomez said in 2010. Rich offerings were tossed into the tunnel at the moment it was closed up, including almost 50,000 objects of jade, stone, shell, and pottery, including ceramic beakers of a kind never found before at the site.

"I think the tunnel was the central element, the main element around which the rest of the ceremonial center was built," Gomez said.

"This was the most sacred place. There is a high possibility that in this place, in the central chamber, we can find the remains of those who ruled Teotihuacan," he added.