About the Battle

At terrible cost, the Battle of Antietam sparked President Lincoln to issue the crucial Emancipation Proclamation from which the Civil War took new meaning for the Union and the world.

If you’re beginning your journey toward an understanding of the battle, welcome! You’re in good company.

Why do we study the battle of Antietam?

The Battle of Antietam was the culmination of the Maryland Campaign of 1862, the first invasion of the North by Confederate General Robert E. Lee and the Army of Northern Virginia. Other Southern armies were marching through Kentucky and Missouri as the tide of war flowed north. After his dramatic victory at the Second Battle of Manassas during the last two days of August, Lee wanted to keep the initiative and secure Southern independence through victory in the North; influence the fall mid-term elections; obtain much needed supplies; move the war out of Virginia, possibly into Pennsylvania; and to liberate Maryland, a Union state.

After the battle of 17 September 1862, however, General Lee’s Army no longer had the strength to continue its invasion of the North and was forced to return to Virginia. Likewise, the other Confederate armies moving north were forced to turn back.

Generations of historians from that day to this have argued what-might-have-been and if you know nothing else about Antietam, you know it was the bloodiest single day in American history.

But beyond its terrible price, the battle is best remembered as the event which sparked President Lincoln to issue the crucial Emancipation Proclamation from which the Civil War took new meaning; for the Union and the world.

Battle Summary

After splashing across the Potomac River, beginning on September 4th and traveling to Frederick, Lee boldly divided his army to capture the Union garrison stationed at Harpers Ferry. Gateway to the Shenandoah Valley, Harpers Ferry was a vital location on the Confederate lines of supply and communication back to Virginia. Gen. Thomas “Stonewall” Jackson and two-thirds of the army were sent to capture Harpers Ferry. The rest of the Confederates moved north and west toward South Mountain and Hagerstown, Maryland. These movements were outlined in Lee’s Special Orders 191.

Back in Washington D.C., President Abraham Lincoln turned to Major General George B. McClellan to protect the capital and respond to the invasion. McClellan quickly reorganized the demoralized Army of the Potomac and advanced towards Lee. His efforts were aided when his men found a copy of Special Orders 191.

The armies first clashed on South Mountain where on September 14 the Confederates tried unsuccessfully to block the Federals at three mountain passes – Turner’s, Fox’s and Crampton’s Gaps. To attack Lee’s widely scattered army and relieve the Harpers Ferry garrison, McClellan had to force his way across South Mountain and by the morning of September 15, his army had done so.

Following the Confederate retreat from South Mountain, Lee considered returning to Virginia. However, with word of Jackson’s capture of Harpers Ferry on the morning of September 15, Lee decided to make a stand at Sharpsburg. With the enemy’s army gathering at Sharpsburg, McClellan had little choice but to move in that direction and prepare to give battle.

The Confederate commander gathered his forces on the high ground west of Antietam Creek with Gen. James Longstreet’s command holding the center and the right while Stonewall Jackson’s men filled in on the left. McClellan spent the rest of September 15 and 16 preparing his plans to attack Lee’s army and drive it back across the Potomac River.

The twelve hour battle began at dawn on the 17th.

McClellan realized that an attack on Lee’s center along the Boonsboro Pike was folly, so he decided to begin the battle by attacking Lee’s left flank. Later in the morning, he would attack Lee’s right and if either of those attacks met with success, McClellan would attack the Confederate center.

The first attack was made by Gen. Joseph Hooker’s First Corps, driving south from the North Woods and aiming for the high ground around the Dunker Church. The two sides encountered each other at the Cornfield and East Woods in intense fighting that lasted about two and a half hours and drew in the Union Twelfth Corps and a host of Confederate reinforcements. By 8:30 a.m., the fighting had all but ended at the Cornfield, as the Confederates had no additional reinforcements to throw into the fray, allowing Union troops to drive south to occupy the desired high ground.

Gen. John Sedgwick’s division of the Second Corps arrived and drove east toward the West Woods. Unbeknownst to these 5,500 men, two Confederate divisions that had participated in the fall of Harpers Ferry garrison had arrived and fell on Sedgwick’s men, causing horrendous casualties and forcing the remainder of the division to flee.

The remainder of the Union Second Corps appeared and drove south toward Sharpsburg, but was stopped by Confederates manning a portion of a Sunken Road, now called the Bloody Lane. Fatigue, dwindling ammunition, and a lack of reinforcements halted the drive toward Sharpsburg.

While the Union assaults were being made on the Sunken Road, a mile-and-a-half farther south, Union general Ambrose Burnside opened the attack on the Confederate right. His first task was to capture the bridge that would later bear his name. A small Confederate force, positioned on higher ground, was able to delay Burnside for three hours. After taking the bridge at about 1:00 p.m., Burnside took two hours to reorganize his Corps and moved it into position to attack Lee’s depleted right flank across arduous terrain. The finally launched attack drove the Confederates from their positions but the timely arrival of Confederate A.P. Hill’s reinforcements from Harpers Ferry saved Lee’s army.

Neither flank of the Confederate army collapsed far enough for McClellan to advance his center attack, leaving a sizable Union force on the sidelines. Despite over 23,000 casualties of
the nearly 100,000 engaged, both armies stubbornly held their ground as the sun set on the devastated landscape. The next day, September 18, the opposing armies gathered their wounded and buried their dead. That night Lee’s army withdrew back across the Potomac to Virginia, ending Lee’s first invasion into the North.


[The maps used here are from the United States Army Center of Military History’s The Maryland and Fredericksburg Campaigns, 1862–1863 by Perry D. Jamieson and Bradford A. Wineman (Washington, DC: USACMH, 2015)]

Recommended reading

On the battle and the Campaign.

Joseph Harsh 

  • Taken at the Flood Robert E. Lee & Confederate Strategy in the Maryland Campaign of 1862, (Kent:  The Kent State University Press, 1999)
  • Confederate Tide Rising Robert E. Lee and the making of Southern Strategy 1861-1862 (Kent: Kent State University Press, 1998)
  • Sounding the Shallows – A Confederate Companion for the Maryland Campaign of 1862 (Kent:  The Kent State University Press, 2000) 

D. Scott Hartwig

  • To Antietam Creek – The Maryland Campaign of September 1862 (Baltimore: John Hopkins University Press, 2012)

Ezra Carman (Dr. Tom Clemens, editor)

  •  The Maryland Campaign of September 1862 Volume 1 – South Mountain. (Savas Beatie, 2010)
  • The Maryland Campaign of September 1862 Volume 2 – Antietam. (Savas Beatie, 2012)
  • The Maryland Campaign of September 1862 Volume 3 – Shepherdstown Ford and the End of the Campaign. (Savas Beatie, 2017) 

Steven Stotelmyer 

  • Too Useful to Sacrifice: Reconsidering George B. McClellan’s Generalship in the Maryland Campaign from South Mountain to Antietam (Savas Beatie 2019) 
  • Bivouacs of the Dead (Toomey Press 1997) 

Ethan Rafuse 

  • McClellan’s War: The Failure of Moderation in the Struggle for the Union (Bloomington:  Indiana University Press, 2005)
  • Antietam, South Mountain & Harpers Ferry – A Battlefield Guide (Lincoln: University of Nebraska Press, 2008) 

Dennis E. Frye

  •  Antietam Revealed (Collingswood, 2004)
  • Antietam Shadows: Mystery, Myth and Machination (Sharpsburg: Antietam Rest Publishing, 2018)
  • September Suspense – Lincoln’s Union in Peril (Harpers Ferry: Antietam Rest Publishing, 2012)

Marion V. Armstrong

  •  Unfurl Those Colors! McClellan, Sumner, & The Second Army Corps in the Antietam Campaign by (Tuscaloosa: University of Alabama Press, 2008)
  • Opposing the Second Corps at Antietam:  The Fight for the Confederate Left and America’s Bloodiest Day (University of Alabama Press, 2016)

Laurence Freiheit

  • Boots and Saddles – Cavalry During the Maryland Campaign (Iowa City: Camp Pope Publishing, 2012) 

Curt Johnson & Richard Anderson, Jr.

  • Artillery Hell, The Employment of Artillery at Antietam (College Station: Texas A&M Univ., 1995)

Brad Gottfried

  •  The Maps of Antietam (Savas Beatie, 2012) 
  • Brigades of Antietam, editor (Antietam Institute, 2021)

Kathleen Ernst

  • Too Afraid to Cry – Maryland Civilians in the Antietam Campaign (Mechanicsburg: Stackpole Books, 1999) 

Alann Schmidt and Terry Barkley

  • September Mourn: The Dunker Church of Antietam (Savas Beatie, 2018)

John Schildt and Gordon Damman

  • Islands of Mercy – Hospitals in the Maryland Campaign (E. Graphics, 2019)

Kevin Pawlak

  • Shepherdstown in the Civil War  (History Press, 2015) 
  • Antietam National Battlefield (Images of America) (Arcadia Publishing, 2019) 

Robert Orrison and Kevin R. Pawlak 

  • To Hazard All: A Guide to the Maryland Campaign, 1862 (Savas Beatie, 2018)

Kevin R. Pawlak and Dan Welch

  • Ohio at Antietam: The Buckeye State’s Sacrifice on America’s Bloodiest Day (History Press, 2021)

John Hoptak 

  • The Battle of South Mountain (Charleston:  The History Press, 2011) 

Tim Reese

  • Sealed With Their Lives The Battle for Crampton’s Gap (Baltimore:  Butternut and Blue, 1998)

Thomas A. McGrath

  • Shepherdstown: Last Clash of the Antietam Campaign September 19-20 1862  (Lynchburg: Schroeder Publications, 2008)

Carol Reardon and Tom Vossler

  • A Field Guide to Antietam (UNC Press, 2016)

Daniel J. Vermilya 

  • That Field of Blood: The Battle of Antietam September 17, 1862 (Savas Beatie, 2018)

James McPherson

  • Crossroads of Freedom: Antietam (New York: Oxford University Press, 2002)

Benjamin F. Cooling 

  • Counter-Thrust From the Peninsula to the Antietam (Lincoln: University of Nebraska Press, 2007)

Gary Gallagher 

  • The Antietam Campaign (Chapel Hill:  The University of North Carolina Press, 1999). 

Ted Alexander

  •  The Battle of Antietam: The Bloodiest Day (Charleston: The History Press, 2011)

Mark Snell

  •  Antietam: The Maryland Campaign of 1862, Vol. 5, No. 3, (Shepherdstown, 1997)
  • The Maryland Campaign of 1862 and its Aftermath, Vol 6, No. 2, (Shepherdstown, 1998)  

John Priest 

  • Antietam: The Soldier’s Battle (New York: Oxford University Press, 1989)
  • Before Antietam: The Battle of South Mountain (Shippensburg: White Mane Publishing, 1992)

Stephen Recker

  • Rare Images of Antietam and the Photographers Who Took Them (Sharpsburg MD: Stephen Recker, 2012)

Joseph Stahl and Matthew Borders

  • Faces of Union Soldiers at Antietam (History Press 2019)
  • Faces of Union Soldiers at South Mountain & Harpers Ferry (History Press 2021)

William Frassanito

  • Antietam, Photographic Legacy of Amerivca’s Bloodiest Day (New York: Charles Scribner’s Sons, 1978) 

Tom Rowland 

  • George McClellan & Civil War History: In the Shadow of Grant and Sherman (Kent: Kent State Press, 1998) 

M. Chris Bryan

  • Cedar Mountain to Antietam: A Civil War Campaign History of the Union XII Corps, July – September 1862 (Savas Beatie, 2022)

Bradley Graham

  • The Antietam Effect (Gettysburg: Media Magic, 2012) 

Scott Mingus

  • Human Interest Stories from Antietam (Colecroft Industries, 2007)

Joe Owen, Philip McBride, and Joe Allport

  • Texans at Antietam (Fonthill Media, 2017)

Cal Schoonover

  • Wisconsin at Antietam: The Badger State’s Sacrifice on America’s Bloodiest Day (History Press, 2020)

Jack Dempsey & Brian James Egen

  • Michigan at Antietam: The Wolverine State’s Sacrifice on America’s Bloodiest Day (History Press, 2015)

John Banks

  • Connecticut Yankees at Antietam (History Press, 2013)

George Large & Joe A. Swisher

  • Battle of Antietam: The Official history by the Battlefield Board (Shippensburg: Burd Street Press, 1998)

Stephen Sears

  • Landscape Turned Red, (New York:  Ticknor & Fields, 1983) 

James Murfin

  • Gleam of Bayonets (Baton Rouge: Louisiana State University Press, 1965)

Phillip Thomas Tucker

  • Burnside’s Bridge: The Climactic Struggle of the 2nd and 20th Georgia at Antietam Creek (Mechanicsburg: Stackpole Books, 2000)

Alexander B, Rossino

  • Their Maryland: The Army of Northern Virginia from the Potomac Crossing to Sharpsburg in September 1862 (Savas Beatie, 2021)