"In 1774, as the situation between Great Britain and the American colonies was heating up, General George Washington inspected a rampart at Roxbury designed by Knox and was instantly taken with the young man's abilities.
Knox soon became Washington's Chief of Artillery, and earned a place in history in the winter of 1776 by carting sixty tons of captured cannon from Fort Ticonderoga in New York to Dorchester Heights, driving the British from Boston Harbor.
Throughout most of the war he was by Washington's side, and eventually rose to Major-General. Following the war he was Washington's choice for the first Secretary at War. They remained life-long friends."
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http://www.generalknoxmuseum.org/knoxbio.html
(It also mentions that 10 of his 13 children did not live to adulthood.)
They appear to have made a mistake on that site in the date of Washington's inspection of the rampart. The General did not arrive in the Boston area until early July, 1775.