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The centuries-old remains of five archbishops of Canterbury were uncovered underneath a London museum by a construction site manager in what historians are calling an "incredible and astonishing" find.

The Garden Museum, which is housed in a church next to the Archbishop of Canterbury's Lambeth Palace, has been closed for two years as construction crews refurbish the building to make room for additional exhibits.

Karl Patten, the site manager for Rooff LTD, had no idea that he would make a major historical discovery when he took on the job. While lifting 3,300-pound stones one day in 2015, contractors came across a concrete block that lay atop a flight of stairs leading to a tomb.

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"We got a camera at the end of a stick and discovered numerous coffins, and one of them had a gold crown on top of it," Patten said in a video posted to the museum's website.

The vault contained 20 coffins, one of which was identified as that of Archbishop of Canterbury Richard Bancroft, who led the committee that produced the King James translation of the Bible in 1611.

Three other identified coffins belonged to John Bettesworth, Dean of the Arches (that is, judge on the ecclesiastical court) for the archbishop of Canterbury from 1710 to 1751; John Moore, the archbishop of Canterbury from 1783 to 1805; and Moore's wife, Catherine.

Museum Director Christopher Woodward said that when he got the call from Patten that day, he was certain that something had gone wrong.

"Every archaeologist in London has looked at this building. But nobody told us to expect to find anything," Woodward said in the video. "I came in thinking, 'This sounds like bad news.' And wow, it's the crown of an archbishop gleaming in the dark."

The church has a long history, having been built in the 11th century by Edward the Confessor's sister across from Westminster Abbey, Woodward said. In the 1960s, the congregation moved and the church was set to be demolished, but a group of volunteers rescued the building and dedicated it as a shrine to a gardener from the 17th century, John Tradescant.

Wesley Kerr, chairman of the Heritage Lottery Fun, which is funding the project, described the discovery as "one of the most incredible things [he's] seen."

"This is really astonishing," Patten said. "To know that possibly the person that commissioned the King James Bible is buried is the most incredible discovery and greatly adds to the texture of this project."