(CNN) — The ruins of an “incredibly rare” 5,000-year-old tomb have been uncovered on one of the Scottish Orkney Islands, National Museums Scotland said in a statement on Tuesday.

The excavation at Holm, East Mainland, Orkney, revealed a stone structure accessed through a 7-meter (23-foot) -long passage and traces of a cairn – or pile of stones – that would have covered it, representing the “pinnacle of Neolithic engineering in northern Britain,” the statement said.

Fourteen articulated skeletons of men, women and children, as well as other human remains, were discovered in one of the six smaller side cells that surrounded a large stone chamber.

“In the Neolithic, it would have been an incredibly impressive 15 meter diameter, enormous mound, very substantial stonework, very impressive architecture. Those cells are real feats of engineering,” Hugo Anderson-Whymark, one of the excavation’s co-directors and senior curator of prehistory (Neolithic) at National Museums Scotland, told CNN.

Two of the skeletons had been positioned so that they were almost embracing against each other, with two children placed over their heads, Anderson-Whymark said. However, archaeologists have not yet determined the relationships between these individuals.

The ruins of an “incredibly rare” 5,000-year-old tomb have been uncovered on one of the Scottish Orkney Islands. (National Museums Scotland)

“The preservation of so many human remains in one part of the monument is amazing, especially since the stone has been mostly robbed for building material,” archaeologist Vicki Cummings, head of the School of History, Archaeology and Religion at Cardiff University, who co-directed the excavation, said in a statement.

“It is incredibly rare to find these tomb deposits, even in well-preserved chambered tombs and these remains will enable new insights into all aspects of these peoples’ lives,” she added.

Only 12 other similar tombs are known to exist in Orkney, referred to as Maes Howe-type passage graves. Most of these remain visible in the landscape – unlike this latest discovery which was buried below ground.

It was largely destroyed in the late 18th or early 19th century to provide stone for building a farmhouse, according to the statement, but later rudimentary excavations in 1896 uncovered eight skeletons and prompted local antiquary James Walls Cursiter to hypothesize that it was a ruined tomb.

Papers held in a private collection of Curister’s notes contained more clues that allowed archaeologists to undertake a geophysical survey in the hope of pinpointing the potential tomb, and provide the basis for the excavation.

“It was quite a surprise to make that discovery,” Anderson-Whymark said. “It’s such a big thing but yet today it’s just a gently rolling field of grass. There’s nothing on the surface to suggest this tomb ever existed there but it would have once been an incredible monument. We’re fortunate they’ve left us just enough of it.”

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