It is a towering testament to a long dead civilisation and has fascinated archaeologists for more than 150 years, but one of the most famous Mayan pyramids has been hiding a secret beneath its mighty steps.

Researchers have discovered an enormous sinkhole beneath the 1,000-year-old Temple of Kukulkan, also known as El Castillo, which dominates the Mayan city of Chichen Itza in the northern Yucatan Peninusula of Mexico.

And they fear the underground cavern, or cenote, which has a river running through it, may eventually cause the entire pyramid to collapse if its roof gives way.

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Archaeologists have discovered the Temple of Kukulkan, which was built by the Maya around 1,000 years ago to worship a snake god, has a huge cenote, or sinkhole, beneath it. They believe it may have been built on top of the cavern deliberately as it may have had deep religious significance to the ancient civilisation

Experts believe the huge chamber may have had special significance for the Mayans, who worshipped at the pyramid, as it is thought to be connected to other sinkhole lakes that surround the pyramid by underground rivers.

It may also be linked to another location known as the High Priest's Grave, or the Ossuary, a smaller pyramid with a sanctuary in the centre which was used as a communal graveyard.

MYSTERY OF EARLY MAYAN KING A stone tablet depicting the reign of a mysterious king in the early days of the Mayan empire has been discovered in ancient ruins in the jungle of Guatemala. The 1,600-year-old tablet, known as a stela, is covered in hieroglyphic writing and dates from a time of great political upheaval in the central Maya area. It was discovered at the site of El Achiotal, which dates to the 5th century AD and is about 12 miles (20km) east of the ruins of the Mayan royal palace of La Corona in Peten, Guatemala. The sites are 40 miles south of the famous Mayan temples at Calakmul in Mexico. The archaeologists have dated the stela to between 22AD and 418 AD. During this period many of the great cities of the Maya civilisation were abandoned. It is a period when there was intense rivalry between two great metropolis of Tikal and and Calakmul. Experts believe the tablet may be depicting the reign of a new king who was appointed by the Tikal after they came to dominate the area. Advertisement

Andrés Tejero-Andrade, one of the archaeologists at Mexico’s National Autonomous University who have been leading the research, said the Mayans may have built the Temple of Kukulkan around 900 to 1,100 years ago on top of the cavern as part of their religious beliefs.

Kukulkan is a Mayan snake deity, or a feathered serpent, who grew up inside and cave before emerging in an earthquake.

Dr Tejero-Andrade said the pyramid may have been built to symbolise the underworld, creation and water.

He said: ‘It appears that El Castillo is dedicated to that element and talk of a water Kukulcan, a snake moving in the water.’

The forming sinkhole beneath the temple is around 82 feet (25 metres) by 114 feet (35 metres) and up to 65 feet deep (20 metres).

The water filling the cavern is thought to run from north to south.

The researchers, who are due to present their findings at an international geophysics conference in Turin in Italy next month, made the discovery using a technique known as an electrical resistance survey.

This uses metal probes inserted into the ground to get a reading for resistance of electrical flow though the ground. Where there is water the resistance changes compared to the rock.

Empty air has a very high resistance reading as the current cannot pass through the air while it is easily transmitted through water.

The researchers say they found there is a layer of limestone about 16ft (5 metres) thick at the top of the cenote, which the pyramid is currently sitting on.

Dr Rene Chavez Segura, a geologist with the National Autonomous University in Mexico, said the high humidity in the cavern and running water could eventually undermine the pyramid.

He said: "Such structures change over time, because the water washed off the walls and the cavity may be increasing.

‘At some point, if the thickness of the rock below the pyramid is thinned, there could be a problem of stability and El Castilla will collapse.’

However, he added this may not happen within his lifetime or even for many generations to come.

The researchers used a technique known as an electrical resistance survey to measure the ground beneath the Temple of Kukulkan. They found a large 65 feet deep cavern beneath the pyramid which has water running through it, as shown in the graphic above. Experts fear it may eventually collapse and destroy the structure

The Maya who built Chichen Itza came to dominate the Yucatan Peninsula in southeast Mexico, shown above

The researchers also found the cenote under the pyramid is also connected to underground caverns and sinkhole lakes to the north, west and east of the pyramid.

Dr Chavez Segura said: "This is not uncommon in a karst soil and the Yucatan.

‘Usually, at depth, the cenotes are interconnected and form a network of tunnels where the water runs free. This forms the natural water network on the peninsula.’

In some areas of Mexico cenotes were used as natural wells or water supplies for ancient civilisations.

The name Chichen Itza also means "at the mouth of the well of the Itza' - the Mayan ethnic group that ruled the area..

Archaeologist Guillermo de Anda, who was not involved in the study, said the underground network of tunnels and caverns may have been symbolic to the Mayans.

Experts say the underground cavern is also connected to other sinkholes and caverns to the north, east and west of the Kukulkan pyramid, including the High Priest's grave, marked El Osario in the map above

The Temple of Kukulcan at Chichen Itza is thought to have been built for the worship of the Mayan snake deity. As a result the water and underground cavern may have been significant in its construction, say experts

WHAT CAUSED THE COLLAPSE OF THE MAYAN CIVILISATION For hundreds of years the Mayans dominated large parts of the Americas until, mysteriously in the 8th and 9th century AD, a large chunk of the Mayan civilisation collapsed. The reason for this collapse has been hotly debated, but now scientists say they might have an answer - an intense drought that lasted a century. Studies of sediments in the Great Blue Hole in Belize suggest a lack of rains caused the disintegration of the Mayan civilisation, and a second dry spell forced them to relocate elsewhere. The theory that a drought led to a decline of the Mayan Classic Period is not entirely new, but the new study co-authored by Dr André Droxler from Rice University in Texas provides fresh evidence for the claims. Dozens of theories have attempted to explain the Classic Maya Collapse, from epidemic diseases to foreign invasion. With his team Dr Droxler found that from 800 to 1000 AD, no more than two tropical cyclones occurred every two decades, when usually there were up to six. This suggests major droughts occurred in these years, possibly leading to famines and unrest among the Mayan people. And they also found that a second drought hit from 1000 to 1100 AD, corresponding to the time that the Mayan city of Chichén Itzá collapsed. Researchers say a climate reversal and drying trend between 660 and 1000 AD triggered political competition, increased warfare, overall sociopolitical instability, and finally, political collapse - known as the Classic Maya Collapse. This was followed by an extended drought between AD 1020 and 1100 that likely corresponded with crop failures, death, famine, migration and, ultimately, the collapse of the Maya population. Advertisement

He said the cenotes that surround the pyramid could represent the four points of the compass.

The river at the center might represent the center of the Maya's universe, which they thought of as a tree with roots reaching below ground.

The National Institute of Anthropology and History also said research at another Mayan site, Uxmal, found an usually high number of medicinal plants growing nearing the structure known as the governor's palace.