 Gage ordered a ditch to be dug in front of the fortifications, that would fill with salt water during high tides, effectively cutting Boston off from the mainland.The neck had soft mud on both sides at low tide, making it very difficult to enter Boston on foot except through the town gate.On the night of April 18, 1775, Patriot leader Doctor Joseph Warren sent Paul Revere and William Dawes on horseback with identical written messages to warn John Hancock and Samuel Adams of the British expedition to capture them and to seize the powder in Concord.