The archaeologists who discovered it believe that it mirrors the Teotihuacans’ great monuments and may represent the underworld in the ancient civilisation’s belief system.
The tunnel is about 10-metres deep and extends from the central square of the ruined city, known as the Plaza de la Luna, to the pyramid.
Archaeologist Verónica Ortega, director of the Integral Conservation Project of the Plaza de la Luna, said: “The finding confirms that Teotihuacans reproduced the same pattern of tunnels associated with their great monuments, whose function had to be the emulation of the underworld.”
A number of explanations have been offered as experts try to determine what the tunnels were used for. Experts believe the tunnel may have been used to simulate the effect of going into the underworld, or it may have been filled with offerings to the gods.
According to one theory, the discovery of the tunnel may only be the beginning.
Youtube channel Secureteam posted a video suggesting that there may be thousands of miles of tunnels across the world which were used by ancient civilisations.
The video explains: “There’s a lot of evidence to suggest that there are miles and miles, possibly stretching across continents and the entire world.
“These tunnelling systems and massive underground cities are said to have once been inhabited by men, animals, families and were basically thriving metropolises.
“It is said that this underworld is where animals, plants and all life originated.”
The discovery was made through a method known as electrical resistivity tomography, which sends scans down through the ground and creates images of what’s beneath the surface.
This isn’t the first secret tunnel to be found at Teotihuacan, which was built some time between the first and 7th century.
Scientists found a 103-metre long one under the nearby Temple of the Feathered Serpent in 2011 and actually ventured down into it, where they found seeds, pottery and the remains of animal bones.
In November 2014, “large quantities” of mercury were found in a chamber around 60 feet below the pyramid, along with jade statues, jaguar remains, a box filled with carved shells and rubber balls.