Dawn approached slowly through the fog on September 17, 1862. As soldiers tried to wipe away the dampness, cannons began to roar, and sheets of flame burst forth from hundreds of rifles, opening a 12-hour battle that swept across the rolling farm fields in western Maryland. This clash between North and South changed the course of the Civil War, helped free over four million Americans, devastated Sharpsburg, and still ranks as the bloodiest one-day battle in American History.

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. In Kentucky and Missouri, Southern armies were also advancing as the tide of war flowed north. After Lee’s dramatic victory at the Second Battle of Manassas during the last two days of August, he wrote to Confederate President Jefferson Davis that “we cannot afford to be idle.”

Lee wanted to keep up the offensive 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, but a slave-holding border state divided in its sympathies.

After splashing across the Potomac River and arriving in Frederick, Virginia, Lee boldly divided his army to capture the Union garrison stationed at Harpers Ferry. The gateway to the Shenandoah Valley, Harpers Ferry, Maryland, was a vital location on the Confederate lines of supply and communication back to Virginia. The 12,000 Union soldiers at Harpers Ferry threatened Lee’s link south. General Thomas Jonathan “Stonewall” Jackson and about half of the Army of Northern Virginia were sent to capture Harpers Ferry. The rest of the Confederates moved north and west toward South Mountain and Hagerstown, Maryland.

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 General Lee. 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.

Following the Confederate retreat from South Mountain, General  Lee considered returning to Virginia. However, with word of Lieutenant General Thomas Jonathan “Stonewall” Jackson’s capture of Harpers Ferry on September 15, General Robert E. Lee decided to make a stand at Sharpsburg.

The Confederate commander gathered his forces on the high ground west of Antietam Creek, with General James Longstreet’s command holding the center and the right. At the same time, General “Stonewall” Jackson’s men filled in on the left. The Confederate position was strengthened with the mobility provided by the Hagerstown Turnpike that ran north and south along Lee’s line; however, there was a risk with the Potomac River behind them and only one crossing back to Virginia. Lee and his men watched the Union army gather on the east side of Antietam Creek.

Thousands of soldiers in blue marched into position throughout September 15th, and 16th as General McClellan prepared for his attempt to drive Lee from Maryland. McClellan’s plan was, in his words, to “attack the enemy’s left,” and when “matters looked favorably,” attack the Confederate right, and “whenever either of those flank movements should be successful to advance our center.” As the opposing forces moved into position during the rainy night of September 16, one Pennsylvanian remembered, “…all realized that there was ugly business and plenty of it just ahead.”

The twelve-hour battle began at dawn on September 17, 1862. There were three major Union attacks on the Confederate left for the next seven hours, moving from north to south. General Joseph Hooker’s command led the first Union assault; then, General Joseph Mansfield’s soldiers attacked, followed by General Edwin Sumner’s men as McClellan’s plan broke down into a series of uncoordinated Union advances. Savage, incomparable combat raged across the Cornfield, East Woods, West Woods, and the Sunken Road as General Lee shifted his men to withstand each of the Union thrusts. After clashing for over eight hours, the Confederates were pushed back but not broken; over 15,000 soldiers were killed or wounded.

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 would be 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 reorganized for two hours before moving forward across the arduous terrain — a critical delay. Finally, the advance started only to be turned back by Confederate General A.P. Hill’s reinforcements that arrived late afternoon from Harpers Ferry.

Neither flank of the Confederate army collapsed far enough for McClellan to advance his center attack, leaving a sizable Union force that never entered the battle. 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. On September 18, 1862, the opposing armies gathered their wounded and buried their dead. That night General Robert E. Lee’s army withdrew back across the Potomac River to Virginia, ending Lee’s first invasion into the north. Lee’s retreat to Virginia provided President Abraham Lincoln the opportunity he had been waiting to issue the preliminary Emancipation Proclamation. Now, the Civil War had a dual purpose of preserving the Union and ending slavery.

The Battle of Antietam was the bloodiest one-day battle in American History. In the end, an estimated 23,100 casualties were suffered.

Today, the Antietam National Battlefield Site is a part of the National Park System and provides several historic sites for visitors and a museum. Films and documentaries are available in the Visitor’s Center. Several tours are available, including a self-guided 8 ½ mile auto tour with 11 stops, self-guided hikes, and Ranger-led talks and walks.

The Antietam National Battlefield Site was established on August 30, 1890, to commemorate the significant events of September 17, 1862, and preserve the battlefield’s important features. Administered by the War Department until 1933, the site was transferred to the U.S. Department of the Interior to be administered by the National Park Service.

The Battle of Antietam was fought over an area of 12 square miles. The site today consists of 184 acres containing approximately 5 miles of paved avenues. Many monuments, markers, and narrative tablets are located along the battlefield avenues to mark battle positions of infantry, artillery, and cavalry. Similar markers describe the actions at Turner’s Gap, Harpers Ferry, and Blackford’s Ford. Key artillery positions on the field of Antietam are marked by cannon. And ten large-scale field exhibits at important points on the field indicate troop positions and battle action.

The National Cemetery, located at the eastern limits of Sharpsburg, is the burial place of Federal dead from the Battles of Antietam, South Mountain, and other minor engagements. Of the 4,773 Civil War burials, 1,836 are listed as unidentified.

More Information:

Antietam National Battlefield
P.O. Box 158
Sharpsburg, Maryland 21782
301-432-5124

Compiled and edited by Kathy Weiser-Alexander/Legends of America, updated October 2021.

Also See: 

Civil War Main Page

Eastern Theater of the Civil War

Maryland Campaign & Battles of the Civil War

Maryland – The Old Line State