On the newly found map, Percy had drawn his route from Lexington to Menotomy and back to Boston. “He's sketching the line of march,” observed local historian Michael Ruderman, studying the new Percy map. “It's the theatre of battle, the hostile territory he had to travel during the afternoon. And he's sketching the landmarks that were significant to him like the Old Powder House tower that he passed on his left."

Percy averted an even greater disaster by marching his 1,700 men by an unexpected route. Rather than continuing straight to Cambridge, he took a left turn to head to the Charlestown neck, where the ships of the Royal Navy could protect his force with their guns and ferry him across the Charles River, back to Boston.

For nearly 250 years, the maps lay forgotten in a box with dozens of other maps of Revolutionary war battles and encampments brought back by Gen. Percy. As the son of the First Duke of Northumberland, he was heir to Alnwick Castle, one of the oldest castles in England. Today the castle welcomes half a million visitors a year, having gained in popularity after serving as a filming location for the Harry Potter movies.

In the Sixties, an earlier team from American Heritage had discovered

Who was the man who amassed this extraordinary collection of maps? David Hackett Fischer described Percy in his book, Paul Revere's Ride:

Lord Percy came by his sympathies for the colonists naturally. His father had voted against the Stamp Act in Parliament, and Percy himself was skeptical about the Crown's handling of the colonial discontent.

The letters in Alnwick Castle provide a fascinating look into the perspective of the British leadership early in the Revolution. Percy had left for his posting in Boston in April of 1774. While waiting at a harbor in Ireland for his troops to catch up, he wrote to a friend that he had been given command of eight regiments. “I fancy severity is intended,” he worried. “Surely the People of Boston are not Mad enough to think of opposing us.”

An hour after arriving in Boston on July 5, 1774, Percy wrote his father that, “I have the misfortune, for I must think it so, of

A few months later, he worried in a letter to a friend that, “Our affairs here are in the most Critical Situation imaginable; Nothing less than the total loss or Conquest of the Colonies must be the End of it. Either indeed is disagreeable, but one or the other is now absolutely necessary.”

Matters grew even worse after colonials dumped tons of tea in Boston harbor in December. On April 8, 1775 Percy reported to his cousin that, “Things now every day begin to grow more & more serious.” He hoped that the recent addresses in both Houses of Parliament had “convinced the Rebels (for we may now legally call them so) that there is no hopes for them but by submitting to Parliament; they have therefore begun seriously to form their Army & have already appointed all the Staff.” 

Nine days later, Percy would find out how serious the rebels were. Among the treasures in Alnwick Castle is a handwritten copy of Percy's report to his superior, Governor Gage, commander-in-chief of the British forces in America at the time. On April 20, the day after the battle, Percy wrote,

The refusal of the rebels to fight a traditional European-style battle greatly frustrated the British. “There was not a stone-wall, or house... from whence the Rebels did not fire upon us,” he told Gage.

Later that day, Percy wrote to his friend, General Harvey,

The Americans, he observed, “have men amongst them who know very well what they are about, having been employed as Rangers agst the Indians & Canadians, & this country being much covd w. wood, and hilly, is very advantageous for their method of fighting.”

Percy's rescue of Col. Francis Smith's panicked troops retreating from Lexington averted what could have been a much worse disaster. But still the British forces that day suffered an estimated 73 killed, 174 wounded, and 53 missing.

For the next two years, Hugh Percy would serve his King honorably, fighting the rebels at Newport, Long Island, and other clashes. He led the British forces in their attack on Fort Washington, capturing nearly 3,000 Americans and dealing them the worst defeat of the war.

Despite his promotion to lieutenant general in 1777, Percy resigned and left the Colonies, provoked by the new commander-in-chief General William Howe and frustrated with the way the British generals were conducting the war.

Returning to England, Percy remarried, had nine children, and inherited the family’s titles and land in 1786. He spent the rest of his life overseeing his vast properties and trying to improve life for the tenants and farmers. He took command of the Percy Yeomanry Regiment in 1798 when Napoleon threatened to invade.

Percy died suddenly in July 1817 from the “rheumatic gout” that had plagued him in his later years. The old general was buried in the Northumberland Vault in Westminster Abbey.