Updated at 1:45 p.m. ET

The accidental destruction of an ancient tomb in northwest Spain was best summed up by an archaeologist in one perfect, if unintended, pun: "monumental error."

Workers in the town of Cristovo de Cea in the Galicia region mistook what is believed to be a 6,000-year-old Neolithic tomb for a broken stone picnic table and "repaired it."

Lauren Frayer reported from Spain for NPR's newscast:

"An ancient tomb in northwest Spain had heritage status — and thus was supposed to be protected and clearly marked as an artifact. But somehow the local town council wasn't aware. So when parks and rec workers saw the granite slabs — they thought they were part of a park bench that needed repair. They poured concrete into the ancient burial chamber, and topped it with a brand new picnic table. An environmental group realized the error and complained. The tomb is believed to be more than 6,000 years old, from the area's ancient Celtic settlers."

An investigation into how the tomb came to be destroyed is underway, according to The Local, but it appears to be an open and shut case: Officials simply weren't aware the site existed — not even the town's mayor, José Luis Valladores.

"No one told me, neither Heritage nor the environmental group," he told the Spanish Huffington Post. "The site wasn't even marked, and the logical thing would have been for them to get in contact with the local council so that we could have taken measures to protect the site," he added.

Juan Barceló, the archaeologist who called the mistake a monumental error, said he "was horrified when he heard [the] news," and speculated that the breakdown in communication between builders and the local authorities was probably due to the summer holidays.

He also told The Local that mistakes like this are not the norm.

"This is not representative of Spain, where monuments over 100 years old are all preserved by law," Barceló said. "All authorities, national, state and local work effectively preserving our heritage. But sometimes accidents happen. I am sure that such disasters happen in many other countries, but have not been published."

It turns out Barceló is partly right. Other countries have destroyed ancient remains, but usually it's done knowingly.

In 2007, as The New York Times reports, "a work crew in the ancient capital city of Nanjing unearthed and destroyed the burial sites of 10 noblemen from six dynasties."

Just last year, according to archaeologists, an ancient Native American burial ground and village in California was discovered and then razed in order to make way for multimillion-dollar homes.

However, the mistaken destruction of ancient relics isn't completely unheard of.

In 2013, NPR's Scott Neuman wrote about workers destroying a 2,300-year-old Mayan pyramid in Belize to use the rubble for road repair. They were apparently unaware that the pyramid was a Mayan ruin.

And then there are times when even the best intentions to preserve ancient relics go horribly awry, like this story from NPR's Eyder Peralta about a painter's attempt to restore a fresco.

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