Workers preparing for the largest sporting event in Qatar’s history have apparently turned up pieces of the Gulf state’s ancient past.

Contractors excavating the area for the Qatar Foundation Stadium in Education City have dug up rocks dating back 20 million to 30 million years, experts said.

The so-called “Dukhan rocks” are gray, light yellow and brown limestone that are part of the Dammam geological formation, which is named after the eastern Saudi Arabian city and make up 70 percent of Qatar’s land surface, according to a 2005 research paper by Qatar University professor Hamad Al-Saad.

In an interview with Doha News, Al-Saad said there is nothing unusual about the rocks being uncovered at the 2022 World Cup construction site.

However, he noted that the stones show Qatar was once covered by the ancient Tethyan Sea:

“The Dammam Foundation in generally represents a period of flooding. That means that area was (once) underwater,” he said.

The findings were announced this week by the Supreme Committee for Delivery and Legacy (SCDL), which is responsible for overseeing the construction of Qatar’s World Cup stadiums and training facilities and also provided more details about the Qatar Foundation facility.

Constructing the venue, which will be used up to the quarter-finals of the football tournament, involves the excavation of 1.37 million cubic meters of rock, which is enough to fill approximately 548 Olympic-sized swimming pools.

Like many modern stadiums, a portion of the facility is being built underground. Once completed, the playing pitch will be between five and six meters below ground level.

This reduces its visual impact on the surrounding landscape and will also help stadium operators keep the facility cool, according to the SCDL.

The QF Stadium is one of eight announced venues that are being refurbished or built from scratch for the tournament. It is scheduled to be completed by 2018, officials said when plans were unveiled slightly more than a year ago.

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