The "Great Ditch" and drainage system (1600s)
The ditch system was dug in the mid-1600s to cut off a loop in the Charles River, and drain the marshy Broad Meadows for use as cattle grazing land. The Great Ditch is still an open canal. The smaller ditches that fed into it are mostly silted up, but can be seen as the darker green lines that cross the meadows. The road at the bottom is Great Plain Avenue, where it crosses into Dedham.
(Image taken from Google Earth)