An 18th-century letter in the vaults of a Michigan library sheds light on the obscure role played by residents of what is now Port Jefferson in the famed Culper spy ring that helped win the Revolutionary War, officials said.

A copy of the letter, which has been known for decades to historians but was little more than a rumor to many village residents, is on display at Port Jefferson Village Hall.

"It's kind of been buried," said local historian Georgette Grier-Key, who helped bring the letter to light and is a consultant to the village on this matter. "It's kind of like it's new again."

The letter, written by a suspected British spy four years after American colonists declared their independence from Great Britain, is owned by the William L. Clements Library at the University of Michigan, which keeps the original in its extensive Revolutionary War collection.

The letter, dated Dec. 21, 1780, accuses brothers Nathaniel and Phillips Roe -- residents of Drowned Meadow, the former name of what is now Port Jefferson -- of helping rebel leader Caleb Brewster of Setauket spy on British troop movements.

The Culper ring, so named for the alias of member Abraham Woodhull, carried secret messages written in invisible ink from Setauket Harbor across the Long Island Sound to Gen. George Washington's upstate New York headquarters. The missive also refers to a place called Old Mans, the former name of what is now Mount Sinai.

Port Jefferson Mayor Margot J. Garant said the letter confirms local legends that the spy ring included residents of Drowned Meadow, so named because the community flooded daily at high tide. Drowned Meadow was renamed Port Jefferson in 1836.

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"Connecting Drowned Meadow to United States history is cool," Garant said. "It was always sort of rumors. We had heard stories. This letter really puts the Roes and Drowned Meadow on the map."

The letter offers a snapshot of the cloak-and-dagger spying that inspired the AMC cable channel series "Turn: Washington's Spies," a fictional account of the Culper ring.

Replete with misspelled names and grammatical errors, the letter was sent by Nehemiah Marks, believed to have been a loyalist spy, to British Maj. Oliver DeLancey, Grier-Key said.

Former Port Jefferson resident Mark Sternberg said he spent years researching links between the Revolution and his hometown before learning in 2013 that the Clements Library had the letter.

"It was really exciting stuff," said Sternberg, an entertainment lawyer and independent movie producer who lives in New York City.

"They were trying to root out our spies," he said. "It sounds like they got a little bit close." BRIDGE OF SPIES

An excerpt from the 1780 letter that historians and local officials say refers to the roles played by Setauket resident Caleb Brewster and Drowned Meadow brothers Nathaniel and Phillipscq Roe in the Culper spy ring:

"This serves to inform you that I have found out where Brewster holds a correspondence of intelligence and who supplied him with goods. I got my information from one that has a commission in the rebel's service, for he tells me that he will do everything to assist me to find out the particular men that send the intelligence from [New] York and he has told me how we might take him if you think it best. ... [A source] informed them Nathaniel Roe for intelligence and Phillip Roe at Round [or Drowned] Meadow for goods, James Smith, at a place called Old Mans. These are the villain that assist Brewster ...

I remain your most obedient servant,

Sent Nehemiah Marks