An ancient palace may have been discovered under a shrine in Iraq that was destroyed by ISIS, archaeologists in the region report, but its tunnels could collapse because of the insurgents' digging methods.

The extra network of chambers, dating back to 600 BC, is beneath the Nebi Yunus shrine in eastern Mosul, where Christians and Muslims believe the tomb of the Prophet Jonah was located, reports The Independent.

Islamic extremists, though, began the digging to the palace after destroying the holy shrine in 2014, marking what may be the first evidence that ISIS is not only destroying historic sites, but plundering the artifacts they discover.

According to researchers, the ancient tunnels house a marble cuneiform inscription showing King Esarhaddon, dating back to 627 BC and the Assyrian empire.

Also, the tunnels contain Assyrian stone sculptures of a demi-goddess, showing the image of the "water of life."

"The objects don't match descriptions of what we thought was down there, so [the destruction of Isis] has actually led us to a fantastic find," said Professor Eleanor Robson, chair of the British Institute for the Study of Iraq, told The Independent.

"There's a huge amount of history down there, not just ornamental stones," she continued. "It is an opportunity to finally map the treasure-house of the world's first great empire, from the period of its greatest success."

However, former Mosul museum curator Layla Salih said she "can only imagine" how much was in the tunnels before ISIS looted them, and before Iraqi forces recaptured the site.

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