Disunion follows the Civil War as it unfolded.

Looking east across Maryland’s Pleasant Valley on Sept. 11, 1862, Polly Yarrow could see men in Confederate gray coming through Brownsville and Crampton’s Gaps in South Mountain and just a few miles from the 10,000 Union troops garrisoned in and around Harpers Ferry. If the Confederates attacked, which seemed likely, they would take the road that ran by her front door.

But that wasn’t her biggest concern. Polly Yarrow was black, and not exactly free. Born a slave on a Maryland plantation outside Washington, she had been living as a free woman ever since marrying Aquilla Yarrow, the son of the most prominent and successful African in Georgetown, Yarrow Mamout. Yarrow (his last name) had come to America on a slave ship. When freed many years later, he became a small-time entrepreneur and financier and the subject of a formal portrait by the eminent painter Charles Willson Peale. After Yarrow’s son married Polly, the couple had moved to Pleasant Valley to be near her brother, who was still a slave. Her husband died a few years after the move, and she had gone to work as a midwife for the community — which was known as Yarrowsburg. Everyone who knew her treated her as free, but she didn’t have the papers to prove it if the invading Confederates asked.

Polly Yarrow was also worried about her brother’s son, Simon Turner. Although technically a slave to a man named Elie Crampton, Turner didn’t live on Crampton’s farm. Instead, he lived with his wife and in-laws on their farm near Yarrow. It was an unusual situation: Turner’s wife, children and in-laws were free, but he wasn’t. African-Americans in Pleasant Valley had to pay attention to such details. Runaway slaves from Virginia regularly crossed the Potomac River at a nearby ford and passed through Maryland on the way to freedom in Pennsylvania. But zealous “Georgia-men,” or slave-catchers, were always on the prowl for the runaways, and they weren’t too particular about whether a slave was from Virginia or Maryland if his owner wasn’t around to claim him.

Yarrow’s freedom was further threatened by local politics. After the 1831 Nat Turner rebellion in Virginia, the Maryland Legislature ordered free blacks and those living as free to register with the county sheriff. This made Polly a marked woman in the event of similar trouble in the future. In the summer of 1859, the abolitionist John Brown arrived and rented a farm on the west side of Solomon’s Gap, a mile and a half from Yarrow’s home. He and his men hid out there for three months before seizing the armory at Harpers Ferry, W.Va., and calling for another slave rebellion. Yarrow surely was questioned by authorities.

Now here came the Confederates.

The soldiers were led by Gen. Lafayette McLaws, who in turn took orders from Gen. Thomas “Stonewall” Jackson. Jackson’s mission was to surround and capture Harpers Ferry to support Robert E. Lee’s invasion of Maryland. McLaws made his headquarters that night in St. Luke’s Episcopal Church, a mile from Yarrow’s house.

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The next morning, Sept. 12, he ordered two brigades of infantry to ascend Solomon’s Gap, passing directly by her home. Though steep and rocky, Elk Ridge isn’t very high there, and the Confederates would have gotten to the top in 10 or 15 minutes if they were unopposed. They in fact met scattered Union resistance but quickly batted it away. Once at the gap, they turned south and flushed Union skirmishers before them as they pushed towards Maryland Heights. While the brigades worked their way along the ridge, McLaws paralleled them on the valley floor.

It’s not clear how Yarrow reacted. If she stayed home, she could have followed the fighting by listening to the sound of gunfire on the ridge above her and by watching the main body of Confederates move along the valley below her. Given her medical skills, she may have been taken to St. Luke’s, which was converted into a Confederate field hospital. More likely, she, Simon Turner and his family and in-laws sought refuge with Turner’s owner, Elie Crampton. Crampton’s farm was on the other side of the valley and well away from the fighting at Solomon’s Gap. There were other reasons for going. “Squire Crampton,” as he was known, was a member of the racially liberal (for the time) American Colonization Society, an officer of the law and a man not to be trifled with, even by Confederate soldiers.

There wasn’t much extra room on his farm, though. Crampton already had four slaves living in a small springhouse just below the main house. That building couldn’t accommodate the seven people Polly would have brought, relatives or not. But there was a bake house nearby, and so the large, extended family could have spread out between the two buildings until the crisis passed.

On their third day in the valley, the Confederates took Maryland Heights. This allowed them to fire down on Harpers Ferry with muskets, but muskets alone weren’t much of a threat. The Confederates needed to get cannons to top of the heights, and this looked to be no small feat. The next morning, Sept. 14, McLaws’s men began cutting a road to the top and by afternoon had hauled four field pieces up and had begun to fire down on Harpers Ferry in earnest. Confederate forces in Virginia took Loudoun Heights, which was just across the Potomac, and opened fire as well. The plight of the Union troops in Harpers Ferry, under cannon fire from the two surrounding heights, looked hopeless. Unless they could be relieved, they would have to surrender.

McLaws had left one brigade at Solomon’s Gap, and the rest of his men were spread throughout the south end of Pleasant Valley. For this reason, Polly Yarrow probably decided to stay at Crampton’s farm even though the fighting appeared finished. McLaws too might have thought the worst was over once he captured Maryland Heights. If so, they both were wrong.

The day before, Sept. 13, McLaws had heard cannon fire from the north and east of Pleasant Valley. Scouts reported large Union forces in those directions. But McLaws dismissed the reports as “questionable.” Then, about noon the next day – even before he had his artillery on top of Maryland Heights – McLaws heard cannonading at Crampton’s Gap, five miles away on the other side of the valley. He quickly rode off to see what was going on.

McLaws had three brigades near the gap, but they were no match for the 15,000 Union troops that came punching through under the command of Gen. William Franklin. After a sharp fight, the Yankees fanned out across Elie Crampton’s farm and then stopped for the night. Polly Yarrow and her charges likely went from the frying pan of Solomon’s Gap into the fire of Crampton’s Gap. Franklin’s decision to rest allowed McLaws to re-form the remnants of his command on a line from about a mile south of Crampton’s Gap across the valley to Solomon’s Gap.

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Franklin’s forces were but a fraction of a much larger Union army under Gen. George B. McClellan. McClellan planned to stop Lee’s invasion and drive his army back across the Potomac River into Virginia. The bulk of McClellan’s men had marched north and west of Pleasant Valley, and they began wheeling south through other gaps in South Mountain in the general direction of Sharpsburg, Md.

McLaws was surprised that Franklin didn’t attack the tiny Confederate force in Pleasant Valley the next morning, Sept.15, but he used the delay to his advantage by resuming the shelling of Harpers Ferry. At 10 a.m., with the big Union relief force under Franklin stalled less than five miles away, the garrison at the ferry raised the white flag of surrender. Stonewall Jackson’s small Confederate army captured not only the town and all its supplies but also the 10,000-man defending force. It was the largest surrender in the history of the United States Army until the Battle of the Bulge in World War II.

By this time, McClellan’s main force was beginning to make contact with Lee’s army at Sharpsburg, and Lee ordered Jackson to wrap things up in Harpers Ferry and join him on the quick. Jackson complied immediately. However, Harpers Ferry held about 500 runaway slaves, who had escaped from Virginia plantations thinking the Union garrison at the ferry would protect them. They were mistaken. Before leaving, Jackson detached an element to march the runaways back to their plantations, turning the Confederate army into Georgia-men.

On Sept. 17, McClellan’s and Lee’s main forces would meet at Sharpsburg along Antietam Creek. McClellan would win. Yarrow and Simon Turner and his family were finally able to return home to Yarrowsburg.

But the interesting part of the saga was just beginning for Yarrow and the Turner clan. Months earlier, President Abraham Lincoln had drafted an Emancipation Proclamation to free the slaves in the South, like those who had sought protection in Harpers Ferry, but he felt he needed a Union victory before announcing it. Seeing the Battle of Antietam as that victory, Lincoln released the proclamation, which was to take effect on Jan. 1, 1863. Still, the Emancipation Proclamation only freed slaves in states in rebellion — i.e., the South. It did nothing for slaves in Maryland, like Simon Turner. But its provisions also allowed African-Americans to serve in the army. Thus, in the spring of 1864, when Union recruiters moved through Western Maryland, enlisting free blacks, Simon Turner decided it was time he did his part. He got his owner to free him and he joined the 39th Regiment, United States Colored Troops.

After the war, Turner returned to Yarrowsburg and the farm his in-laws owned, where he raised a family. Although Turner and his wife were illiterate, they helped start the first school for blacks in the valley. It was segregated, of course. Their children went there, including a daughter named Emma, Polly Yarrow’s great-niece. Emma went on to get a degree in teaching from Storer College in Harpers Ferry, the town Stonewall Jackson had once taken.

Emma’s son, Robert Turner Ford, was admitted to Harvard in 1923, and he graduated in 1927. Polly Yarrow was his great-great-aunt and Simon Turner his grandfather. They had witnessed the Battles of Crampton’s Gap, Harpers Ferry and Antietam. In a very real and personal way for this family, those battles led to the Emancipation Proclamation, freedom and, eventually, the pinnacle of American education.

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James H. Johnston is the author of “From Slave Ship to Harvard: Yarrow Mamout and the History of an African American Family.”