Rick Green: May 26, 1673, the day of the Pequot Massacre
"The surprise attack by Capt. John Mason, along with Mohegan warriors, began before dawn on May 26, 1637. Mason set fire to an Indian village along the Mystic River killing at least 500, most of them women and children.

Mason's attack and the subsequent Pequot War decimated the tribe, which waited (some say it disappeared) for 350 years before the world's largest casino brought them back to prominence. The Mohegans, the Pequots' historic enemy and ally of the British, now operate their own Mohegan Sun casino

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From an account by Capt. John Underhill:

Many were burnt in the fort, both men, women, children. Others forced out, and came in troops to the Indians, twenty and thirty at a time, which our soldiers received and entertained with the point of the sword. Down fell men, women, children; those that scaped us, fell into the hands of the Indians that were in the rear of us. It is reported by themselves, that there were about four hundred souls in this fort, and not about five of them escaped out of our hands."

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Rick Green: 373 Years Ago Today, John Mason Led the Pequot Massacre (The Hartford Courant 5/26)