The North Bridge
This picture is from the north side of the bridge. This is the angle from which the Minutemen marched. The terrain integrity here, excluding the momuments of course, is fairly good. The main exception is the number of trees. On the left and right of the bridge you can see the number of tree's in the photo. In 1775 you could see from the North bridge to the center of Concord located to the right of the bridge.
The second major terrain difference is the angle of the road in which the the colonials march down. Currently that road approaches the bridge with no angle. In 1775 this road angled obliquely to the bridge, giving the milita a huge field of fire on the mass of British troops.