Ancient tunnels believed to be ‘entrances to the underworld’ have been found running deep into the ground beneath a centuries-old church.

Mitla, meaning place of the dead, was a city in southern Mexico known for its association with Pitao Bezelao, the Zapotec god of death.

But the Spanish came in the 16th century and razed the city and built a church on the ruins of the most important temple.

A priest later wrote that there was a ‘back door to hell’ beneath the city; these huge caves were believed to be the entrance to the Zapotec underworld.

However, he said they were surrounded by walls, and subsequent excavations have so far found nothing matching his description.

Using non-invasive techniques, archaeologists recently uncovered a series of chambers and tunnels beneath the city.

Five different groups of ruins were investigated: the church group, the arroyo group, the adobe group, the south group, and the column group.

Marco Vigato, founder of the ARX Project, which led the search, said: ‘Some tunnels and chambers extend to a significant depth of over 15 metres.

Ancient tunnels believed to be ‘entrances to the underworld’ have been found beneath a centuries-old church, delving deeper into the earth

Archaeologists recently uncovered a series of chambers and tunnels beneath the city using non-invasive techniques

Archaeologists have uncovered what they call the ‘back door to hell’ in tunnels beneath an ancient church (stock image)

‘In the case of the southern group, they are up to 30 meters deep; this is the distance the tools can penetrate.

‘A room under the Church of San Pablo Apostol is approximately 15 meters long and 10 meters wide.

‘It is possible that the tunnels, especially those under the church group, extend north, east and south.

‘They are probably linked to other geophysical anomalies identified under other groups.’

If these are legendary tunnels, Zapotec kings may lie inside.

The aforementioned priest Francisco de Burgoa draws a picture of the royal burial chamber in his 1674 text Geografica Descripción.

He says the kings were buried ‘richly dressed in their best clothes’ with ‘feathers, jewels, gold necklaces and precious stones’.

Meanwhile, their bodies hold ‘a shield in their left hand and a javelin in their right hand, just like they used in battle.’

Five different groups of ruins were investigated: the church group, the arroyo group, the adobe group, the south group, and the column group.

The underground tunnels were revealed using a combination of ground-penetrating radar, electrical resistivity tomography and seismic noise tomography.

Seismic noise tomography measures the speed at which seismic waves travel through the ground instead of electricity

The other two caves he describes contain a chapel and a burial chamber for Zapotec high priests, respectively.

The last room, he says, opened into a ‘dark and terrible chamber’ into which ‘the bodies of the battle victims of great lords and chieftains were thrown’.

Mr Vigato said: ‘The Zapotecs believed that the caves and underground labyrinth beneath Mitla were the entrance to the underworld, or Lyobaa.

‘Mitla was therefore the center of the cult of Pitao Bezelao, the Zapotec god of death and the underworld, and for centuries the burial ground of Zapotec kings and high priests.’

It is no coincidence that there is a gap under the church altar.

Mr Vigato said: ‘The church was deliberately built over the most important Zapotec temple at Mitla.

‘This was a way of transforming a pre-existing religious site and symbolizing the triumph of the new faith.

‘A significant part of the ruins was included in the foundations of the church, which was built with stones removed from ancient buildings.’

The underground tunnels were revealed using a combination of ground-penetrating radar, electrical resistivity tomography and seismic noise tomography.

This photo shows the interior of the San Pablo Apostolic Church in Mitla

Researchers now hope to determine the nature of the cavities detected beneath the site and whether they contain any artifacts of archaeological significance.

The first method uses radar waves to model the subsurface, while the second detects buried structures by measuring the electrical flow underground.

The last method measures the speed at which seismic waves travel through the ground instead of electricity.

It has not yet been determined how old the tunnels are.

Mr Vigato said: ‘The natural caves in the Mitla area have been occupied and partially modified by humans for thousands of years.

‘The earliest evidence of domestication of crops in the Mitla region dates back almost 10,000 years.

‘There is currently no indication of the possible age of the tunnels under the church or other groups of structures at Mitla.

‘They may have been created by the Zapotecs, or they may be much older.’

He added: ‘Findings from geophysical surveys will need to be confirmed by archaeological methods.

‘This could determine the nature of the cavities detected beneath the site and whether they contain any artefacts of archaeological significance.’

You can learn more about the discoveries at Mitla at: www.arxproject.org.