CORNISH – Firefighters say they may never know what caused a weekend blaze that leveled a historic 19th century mansion that once was home to the only U.S. Supreme Court justice from Maine.

The 5,400-square-foot dwelling on High Street burned to the ground Sunday, leaving a pile of splintered timbers, charred carpets and twisted sheets of steel roofing.

Rob Puncheon, who owned the home for the last 15 years, said the fire began in the barn, then spread to the ell and finally to the house itself.

“I looked out the window and the upper stories of the barn were in flames,” Puncheon said. “When something that old is lit up, there is not much you can do.”

The cause of the fire is still unknown and may never be determined, said firefighter Tom Pingree.

“We have just lost one of our greatest treasures,” said Stephen DiBiaso, a lifelong Cornish resident who saw the flames from his house a mile down the road.

Built for a wealthy farmer who moved to Cornish from New Hampshire in 1820, the house was the last home of Nathan Clifford, who served in Congress and as attorney general before being appointed to the Supreme Court in 1858.

Different generations of Cornish residents called the house by different names. For some, it is the Clark Farm.

Others knew it as the Chick Farm or the Tanguay place. For the past 15 years, it has been known as Halcyon Farm, the name it was given by Puncheon and his partner, Gary Hamelin, who restored the house to its former glory.

The outside was Greek Revival, but the interior used the more ornate Italianate style. The main house featured a 30-foot-long, three-story high central hall. The ell housed a 20-foot-by-20-foot gourmet kitchen Puncheon used for his catering business, and connected to a four-story barn, 200 feet long.

It was last used as a working farm in the 1970s, DiBiaso said. Over the years, the house was divided into apartments and was neglected. “It suffered some real down times until Rob and Gary bought it,” he said.