Burnside's Bridge, from the steep bluffs the Confederates defended.
The Cornfield, Bloody Lane, and Burnside's Bridge. Three sites of carnage never seen before... or after.
Keith Snider, a park ranger at the Antietam Battlefield, has been giving tours of it for decades.
"You have two determined armies that are going to try to destroy each other starting at 5:30 in the morning," he says. "And the point of contact if you will is the famous cornfield."
The cornfield was the left flank of the Confederate Army, and Union General George McClellan wanted to attack both flanks of General Robert E. Lee's famed Army of Northern Virginia.
"Which is sort of the standard military tactics for the Civil War period," says Snider. "No one wants to make frontal assaults against the weapons of the day."
McClellan was never known for moving his army quickly and committing it to battle. "I would say that he loves his men... maybe too much. I kind of like that in a commander."
But McClellan did speed up in this case after discovering a copy of Lee's battle plans. And at 5:30 on the morning of Sept. 17, Union soldiers attacked the Confederates in the Cornfield.
"Men described as a 'savage, continual thunder that cannot compare to any sound ever heard.' One of the Texans that fought there, from the famous Texans of Hood's brigade, described it as the 'dogs of war were loose and havoc was their cry.' It's hand to hand... almost all of the combat in the cornfield was done from 100 yards and closer."
It wasn't all valor in the Cornfield, as one Union brigade commander proved.
"Col. Christian, who as the battle begins in the thunder of artillery, the avalanche of lead and iron... he runs away," explains Snider. "He leaves his men. He's court martialed, dies in an insane asylum. He's responsible for 2,000 men, and he runs away."
On a day of savage fighting, the Cornfield saw the worst.
"You have approximately 10,000 men killed or wounded by 9:30 in the morning. You average just those casualties... it's a man killed or wounded every second for four hours."
There were 10,000 casualties, with about 25,000 men involved, says Snider. The fighting then moved to the center of the Confederate line and an area called Bloody Lane.
"The fighting there starts around 9:45, and will last about 3 to 3.5 hours," he says. "It's an old country farm lane that over the years had been worn down. Its 6 to 8 feet deep, and it made a perfect defense position for the southerners."
Just like in the Cornfield, superior Union forces wore down the outnumbered Confederates, but slowly and at great cost.
"When the Union soldiers had to attack the lane, they had to come across open ground, so they're walking into an entrenched position, and when they appear they're only 60-70 yards away. Almost like a fan belt of Union brigades trying to break through.
"So many men are lost trying to break and capture the lane, that it's virtually impossible to follow up on. So once again, it quiets down in the center, and you have another 5,000 killed or wounded and the battle lines moved 150 yards."
Having attacked the left and center, the Union then went after the Confederates right, targeting Burnside's Bridge, since renamed after the Northern general who led the attack.
"The farther south you go on the battlefield, the worse the terrain gets," continues Snider. "The gulleys are deeper, the knolls are taller. And of course, right at the bridge, there are the bluffs that make it almost impregnable."
Very slowly, the Union crossed the bridge and pushed the southerners back to Sharpsburg.
"Once again, the Confederates have a great terrain advantage. There's 80-foot high bluffs, it's like a fortress. Burnside has to send in a series of attacks to get that crucial Antietam crossing."
The delay in getting across ended up undoing the North, as Confederate reinforcements from Harpers Ferry arrived just in time to send the Union back across the bridge.
"Union soldiers are almost to Sharpsburg, with victory in their grasp, and that's when they're driven back. And there are accounts of men being ordered back literally with tears in their eyes for having to give up such hard fought ground."
"At about 5:30, 6 o'clock, the battle slowly fades like a shower," says Snider. "The last few drops, the last few pops of rifle fire."
The immediate aftermath was "pure shock."
"There's never been a day like this before or since in American military history," says Snider. "I don't think at the end of the day anybody knows where anybody is, or can even begin to fathom what has just happened."
But the generals soon begin to get word what did happen: 23,000 men are dead and wounded in the single bloodiest day in U.S. history.
"Lee was trying to make a point that he wasn't driven from the battlefield," says Snider. "But then he got the reports that he has lost 25 percent of his army. He realizes he has to get back to Virginia."
In the days ahead, the Southern army did return home.
"You could argue that Antietam was tactically a draw. But Abraham Lincoln makes it a great strategic victory. Not only for the army, but for the nation, and for the future."
Five days after the battle, President Lincoln issued the preliminary Emancipation Proclamation, eventually freeing more than 3 million people held in slavery.
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