This is a reference to an incident occurring in 1776 at the start of the Revolutionary War. Having been victorious in the Battles of Lexington and Concord, the British forces held control of Boston but found themselves closely besieged by George Washington’s Patriots. The future first president ordered his artillery commander to bring a cannon to Dorchester Heights, which he duly did, dragging the hefty ordnance across miles of snow-covered, roadless ground. The Patriots worked secretly through the night to establish their weaponry and, when the British awoke to see the entire of Boston essentially under the domination of their enemies, they and their supporters had no choice but to evacuate. Halifax, Nova Scotia, was the place to which they fled.