|Illustration 1. Looking north|
from "B" in Illustration 2.
In the foreground of this well known photo are the remains of a fence (Illustration 1. Click on all images on this page to enlarge).
William Frassinito, in his photographic study of Antietam remarked of this photograph: "Today the ground over which these units charged appears much as it did in 1862. According to official maps, the rails scattered about the foreground in view 4 marked a fence line." 
According to the Cope-Carman 1908 map, the fence was a post and rail fence similar to that which bordered the Hagerstown Turnpike (Illustration 2).
Closer examination of the fence remnants in the Gardner photo brings this into question.
In the Gardner photo, the fence rails appear to have come from a wormwood fence and not that of a post and rail fence.
|Illustration 3. Detail from|
Another view of the field, this one a reverse view taken from north of the wrecked caisson, shows the scattered rails (Illustration 6). Although less clear (the original photo has been lost), the scattered rails and the lack of posts, which would have been left standing even if the horizontal rails had been brought down, further suggests that the fence was a worm wood one.
While there have been interesting studies on the effect of topography and geology on the field and on the movement of units, to my knowledge nothing has been written about the effects of more serious barriers--fences.
Many first hand accounts mention fences--the stone fence near the Miller farmstead served as a rallying point for the First Minnesota and other units; the thrown-down (apparently) worm wood fence along the Hagerstown Pike north of Smoketown Road (see the second post in this series) provided Confederate infantry an avenue to and from the West Woods.
|Illustration 5. Post and rail fence|
The movement of artillery, at the least, would be governed by the type of fence in front of it--stone and post and rail would be obstacles while a worm wood fence could be thrown down and batteries placed (as appears to be the case with S.D. Lee's battery). 
Somehow, I think that there is something about fences that might make an interesting line of inquiry. Who knows, it might give us some additional insights into the events of September 17th.
This short "fence" series was inspired in part by a conversation with Dave McGowan about fences laying between the Smoketown Road and the Cornfield.
|Illustration 6. Looking south|
from "A" in Illustration 2.
 Frassanito notes: "The negative for this Antietam photograph has not survived, and I have never been able to discover a contemporary print. ... [T]he only known photographic reproduction currently available is that which appeared in Francis Miller's ten-volume Photographic History of the Civil War (1911)." pp. 169-70.
 See, for example, BG John Walker's official report in which he describes Manning's advance through the fields beyond the West Woods: "Colonel Manning, with the Forty-sixth and Forty-eighth North Carolina and Thirtieth Virginia, not content with the possession of the woods, dashed forward in gallant style, crossed the open fields beyond, driving the enemy before him like sheep, until, arriving at a long line of strong post and rail fences, behind which heavy masses of the enemy's infantry were lying, their advance was checked; and it being impossible to climb over these fences under such fire, these regiments, after suffering a heavy loss, were compelled to fall back to the woods ..." Retrieved from Antietam on the Web (www.aotw.org).
Group III-4 Near the Dunker Church [Frassanito], view looking north, Gardner, stereo #568, September 19, 1862, Library of Congress."
Group III-5 Dead artillery horses, view looking southwest toward the Hagerstown Pike [Frassanito]. Gardner, stereo #564 September 19, 1862, Miller, Photographic History of the Civil War, pp. 169-70.