​The 1814 burning of Washington, D.C.

Moving from the Capitol, British Navy Rear Admiral George Cockburn, Army Major General Robert Ross, and 150 redcoats marched to the White House.

Rocca asked Allman what the Britons' impression of the White House would have been as they walked in the door: "I think that it was a pretty good-sized house, but not a palatial one. No Buckingham Palace. No Versailles. That it was, you know, reasonably well decorated."

The biggest surprise? A dinner set for 40. So the British feasted in the White House dining room before burning the mansion down.

Here, too, the walls survived. But little remains of what was once inside -- what does is an American icon.

The East Room, the largest room in the house, and where Teddy Roosevelt's kids used to roller-skate; where Susan Ford had her senior prom; and more importantly, the room with the great full-length portrait of George Washington by Gilbert Stuart.

"This is the one that Dolley Madison rather famously saved before leaving the White House. She had already packed up state papers, the red velvet drapes that she had had put in the Oval Room. Then, kind of as a last-minute thing, she said, 'Oh, we've got to save General Washington.'"

"And she gave the instructions to get it off the wall. It was bolted on. So they had to pretty much cut the frame open and then lift the canvas out on its stretcher."

As Dolley Madison was busy cramming silverware into her purse, White House servants -- the maitre d' and one of the family's slaves -- rescued the painting. "She was trying to save everything she could," said Allman. "She was leaving her personal things."

As a rule the British invaders didn't loot, but one soldier grabbed Madison's personal traveling medicine chest. "That was taken from the White House by one of the British troops, later passed to a member of one of the naval forces, and then descended in his family until it was given to Franklin Roosevelt in 1939," said Allman.

After torching the White House, the redcoats burned the buildings housing the Departments of State, Treasury and War, concluding one of the most devastating days in American history.

Rear Admiral George Cockburn (1772-1853), by John James Halls. Royal Museums Greenwich

"Can you imagine the scene after the British have departed Washington?" said Vogel. "The Capitol and the White House are smoldering shells. The American Army has abandoned the city. Nobody knows where President Madison or the cabinet are. It's really impossible to think of many more despondent, desperate moments in American history."

As a Union Jack flew over the city, Vogel said, "A lot of people felt that, you know, the young republic was coming to its end, that the American experiment was dying in its infancy."

Fearing an American counterattack, the British occupation of Washington lasted only a day.

Among its overlooked heroes: State Department clerk Stephen Pleasonton, who hid the Declaration of Independence in a Virginia mansion.

Six months later, the war ended in a virtual stalemate, and British leader George Cockburn returned home, where his portrait features Washington blazing in the background.

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