Ball’s Bluff could fit into the back pocket of Antietam or Gettysburg. It’s tucked behind a residential neighborhood in Leesburg, lurking in the woods at the end of a gravel road. Like all Civil War battlefields, it’s dramatically unlike the Civil War itself. It’s quiet. The cannons are harmless, as inert as stumps. The old cowpaths have been converted to hiking trails and dutifully mulched. There’s hardly anyone around. You could nap on a blanket.

It is the visitor’s challenge to figure out how to read this landscape, how to see it the way the generals did. Add people, noise, smoke, wails, the rebel yell, the whistle of bullets. Add mud.

At Ball’s Bluff, you can walk down a trail, past a small national cemetery, and eventually come to a precipice. About 120 feet below, visible through the early fall foliage, is the Potomac River.

Here, on Oct. 21, 1861, the Union engineered an epic fiasco.

The federals crossed the river into Virginia, seeking to make “a slight demonstration” against an unknown number of rebels believed camped nearby. The Union soldiers had only a few skiffs for the crossing. It was an immaculate setup for a tragedy: sketchy information, a river too deep to ford, not enough boats, and soldiers who couldn’t swim.

Ball’s Bluff is the tale of a quick, tidy slaughter. It contains broader lessons about warfare, painfully learned as the bodies floated downstream.

The river factor

We think of 19th-century wars as set-piece battles, with armies colliding in cornfields and peach orchards, the soldiers demonstrating their valor as they charge the opposing line. But the generals knew there was more to it than that. They knew that success or failure in the war would depend on logistics, on supplies, on feeding men and mules, on lines of communication, on knowledge of the landscape and precision of the maps.

What they saw as they examined the Coastal Survey maps was a vast territory dominated by rivers. Much of the war was contested on rivers, along their muddy banks, and at the bottlenecks of their bridges.

Rivers were still thoroughfares in 1861. There weren’t many bridges then, or even decent roads. As John Keegan writes in “Fields of Battle,” during the Civil War “roads were still conceived as part of an internal waterway-portage system, harking back to the wilderness days of the eighteenth century.” Roads often ended at the bank of a river, without a bridge. You were expected to switch to a boat.

Rivers shaped the war both strategically and tactically. The Union’s initial goal was to encircle the Confederacy by blockading the coast with the burgeoning U.S. Navy (the number of naval vessels grew dramatically in the first year of the war) and by gaining full control of the Ohio and Mississippi rivers. The encirclement strategy came from the old man who initially led the Union military, Mexican War hero Gen. Winfield Scott. “Scott’s Anaconda,” it was sometimes derisively called.

The rivers in the West served the Union well: Not only did the Mississippi cleave the Confederacy and, once controlled, cut off the eastern states from the vast resources of Texas and other western states, but the Tennessee and Cumberland rivers invited invasion of the heart of rebel territory. It was an invitation that Ulysses S. Grant happily accepted when he led his soldiers on steamers up the Tennessee River in early 1862 and, with help from Navy ironclads, took Fort Henry and then Fort Donelson — unmitigated Union victories.

The rivers of the east presented a different story. They were obstacles, as a rule, for maneuvering armies, generally flowing from west to east, and some would loom large in history despite their modest scale (such as the Rapidan, the Rappahannock and the Chickahominy). The historian James McPherson says, “The rivers in the Eastern theater helped the defense, and that means the Confederacy for the most part.”

So central were the rivers to the conduct of the war that military units (particularly on the Union side) were named for them: the Army of the Potomac, the Army of the Cumberland, the Division of the Rappahannock, the Division of the Ohio and so on.

The Potomac was famously eccentric — alternately impassable with floodwaters and dried to a trickle. Low water helped Robert E. Lee’s invasion of Maryland in the late summer of 1862, but floodwaters the next summer nearly trapped his army after the Battle of Gettysburg, and he was lucky to escape across makeshift bridges near Williamsport, Md.

The Potomac carried symbolic importance as the boundary between loyal and rebellious states, and it served as a moat for the U.S. capital, consciously seated by the Founding Fathers in a slaveholding territory, and in 1861 facing a Confederate army just 25 miles away in Manassas.

“As soon as secession happened, the Potomac became the most important river in the Civil War,” said Jonathan Earle, an associate professor of history at the University of Kansas. “The Potomac was a psychological border as well as a physical one.”

The bridge over the Potomac at Harpers Ferry, W.Va., was burned repeatedly during the war. Engineers mastered the art of laying a pontoon bridge in a matter of hours — essentially placing planks across boats that had been lashed together. But this proved to be a bloody craft at Fredericksburg, as the rebels mowed down the engineers building the bridges for Gen. Ambrose Burnside’s army.

Union Gen. George McClellan discovered, in his Peninsula Campaign of 1862, that a heavy rain — “Confederate weather” — could transform a minor tributary such as the Warwick River, which flows into the James, into an almost insuperable barrier. And here’s McClellan writing of the Chickahominy as though it were the Nile or the Amazon:

“It was subject to frequent, sudden, and great variations in the volume of water, and a single violent storm of brief duration sufficed to cause an overflow of the bottom-lands for many days, rendering the river absolutely impassable without long and strong bridges.”

McClellan was a world-class worrier, always imagining that he was outnumbered and, in this instance, outrivered. Lincoln nearly went mad trying to get McClellan to attack. “But you must act,” Lincoln said in closing one chastising letter in early 1862. McClellan, however, understood the principles of military strategy and was quite correct that attacking without a good plan and proper logistics was a recipe for disaster.

Which was what happened amid the autumn leaves in October 1861 at Ball’s Bluff.

‘A slight demonstration’

McClellan that fall was in the mode of army-building, getting everyone trained, trying to avoid a repeat of the debacle at Manassas in July. One day he learned that Confederates were deployed near Leesburg not far from the Potomac River. McClellan didn’t want to lose control of the upriver Potomac and the critical Baltimore & Ohio Railroad that passed through Point of Rocks, Md., and Harpers Ferry. McClellan wired Gen. Charles P. Stone, camped in Poolesville, Md., suggesting that “perhaps a slight demonstration on your part would have the effect to move them.”

Stone sent three regiments across the river, one at Ball’s Bluff and two at Edwards Ferry a few miles downriver. There wasn’t a bridge anywhere along that stretch of the river, and it was too deep to ford, so they had to rely on boats. Only three were available at Harrison’s Island, a two-mile sickle of land occupying a bend in the Potomac facing Ball’s Bluff. Stone sent a note to McClellan: “We are a little short of boats.”

They were also a little short of professional soldiers. The man who quickly took command on the bluff was a sitting U.S. senator from the young state of Oregon. Col. Edward Baker was an advocate of “bold” and “determined” war and a close friend of the president (Lincoln’s second son was named for him). Baker was gifted at oratory but impoverished in military strategy. That the Union forces were backed up to a bluff above a river, with only a few skiffs available in the event of a retreat, did not faze him.

When a New York regiment ascended the cow path up the bluff, Baker greeted a newly arrived colonel with a quotation from “The Lady of the Lake”: One blast upon your bugle horn/ Is worth a thousand men.

Unbeknownst to Baker, the Confederate commander, Gen. Nathan G. “Shanks” Evans, had sent his men from Edwards Ferry to Ball’s Bluff. The rebels had superior position in the woods, picking off Baker’s men as they struggled to hold their ground. Baker himself began working artillery pieces. The rebels charged, whooping, and the fight was joined hand to hand.

The New York World reported what happened next:

“One huge red-haired ruffian drew a revolver, came close to Baker, and fired four balls at the general’s head, every one of which took effect, and a glorious soul fled through their ghastly openings.”

Historian Shelby Foote writes: “[H]e who called for sudden, bold, forward, determined war received it in the form of a bullet through the brain, which left him not even time for a dying quotation.”

In pell-mell flight, hundreds of Union soldiers scrambled, stumbled and somersaulted down the steep bluff. So many boarded a flatboat that it foundered. Soon all three skiffs had sunk.

Rebels stood atop the bluff and fired at the men below. It was, the rebels would say later, like a turkey shoot.

Whom the bullets didn’t kill, the water did. Dozens of men drowned. Americans, as a rule, couldn’t swim in 1861. They couldn’t have stayed afloat even if they hadn’t been burdened by wool uniforms, boots and heavy weapons.

Of valor the federals had plenty; what they lacked were boats and trained officers who could read a landscape. Ball’s Bluff inspired Congress to create the Joint Committee on the Conduct of the War. It was a star chamber, secretive, radical, and its first victim was Gen. Charles P. Stone, accused unjustly and irrationally of treason and thrown without formal charges into a prison cell in New York harbor. Stone was eventually released and returned to the Union cause, but his reputation never fully recovered from the Ball’s Bluff calamity.

The battle offered an immediate lesson about the importance of military principles, of logistics, of avenues of retreat. Coming after Manassas, it boded ill for a quick suppression of the Confederacy. Anyone in Washington who remained unclear about the challenge facing the Union needed merely to visit the banks of the river. The bodies were washing up. One at Chain Bridge, one at Long Bridge, one all the way down near Mount Vernon.

This was going to be a very long war.

This story was included in a Washington Post special section, “Civil War 150: Ripples of War.” See more stories on the Civil War.