There are several good stories about the map. Start with this one from the Library of Congress, who keep the map. And a more local perspective from the NPS Minuteman Park, and Baahston Marathon Day,
Leaving Boston in a hurry on Evacuation Day in 1776, Ensign De Berniere left several papers that were then publsihed as General Gage's Instructions and a curious narrative. These are quoted here.
February 1775. Su Mo Tu We Th Fr Sa 19 20 21 22 23 24 25 29 30 31 1 2 3 4
Wednesday, March 1st, starting from the Golden Ball in Weston.
"- At two o'clock it ceased snowing a little, and we resolved to set off for Marlborough, which was about sixteen miles off; we found the roads very bad, every step up to our ankles ; we passed through Sudbury, a very large village, near a mile long, the causeway lies across a great swamp, or overflowing of the river Sudbury, and commanded by a high ground on the opposite side; nobody took the least notice of us until we arrived within three miles of Marlborough, (it was snowing hard all the while) when a horseman overtook us and asked us from whence we came, we said from Weston."
Thursday, March 2nd, having left Marlborough abruptly at 10:30PM after being warned of impending danger.
"we got without being perceived, as
far as the hills that command the causeway at Sudbury,
and went into a little wood where we eat a bit of bread
that we took from Mr. Barnes's, and eat a little snow to
wash it down. -- After that we proceeded about one hun-
dred yards, when a man came out of a house and said
those words to Capt. Brown, "What do you think will
become of you now," which startled us a good deal,
thinking we were betrayed. -- We resolved to push on at
all hazards, but expected to be attacked on the causeway ;
however we met no body there, so began to think it was
resolved to stop us in Sudbury, which town we entered
when we passed the causeway ; about a quarter of a mile
in the town we met three or four horsemen, from whom
we expected a few shot, when we came nigh they opened
to the right and left and quite crossed the road, howe-
ver they let us pass through them without taking any no-
tice, their opening being only chance ; but our appre-
hensions made us interpret every thing against us. -- At
last we arrived at our friend Jones's again, very much
fatigued, after walking thirty-two miles between two
o'clock and half-after ten at night, through a road that
every step we sunk up to the ankles, and it blowing and
drifting snow all the way."
The long causeway commanded by a high ground is now Rte 27.
J.L. Bell has a blog called Boston 1775 with stories about the spies stay at the Golden Ball, thoughts about map, Ensign Henry DeBerniere, and Capt. William Browne.
Brown & DeBerniere probably took Old Connecticut Path twixt Weston & Framingham on 2/24 and 2/28. That went thru Sudbury at the time, as the town did not split until 1780. More: evolution of town bounds.
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