This is why Washington wasn't relentlessly attacked by the Confederates
The distance between Washington, D.C. and the former Confederate capital of Richmond, Va. is a scant 95 miles. They're practically neighbors. Early in the Civil War, the Union Army attempted to capture the rebel capital but the forces led by Gen. George McClellan only made it as far as the suburbs before being beaten back. Richmond wouldn't fall to the Union Army until 1865 – but it wasn't through lack of trying.
Meanwhile, the District of Columbia sat precariously perched between rebel Virginia and border slave state Maryland. It was the heart and nerve center of the Union but aside from the threat of an advancing enemy, it wasn't as constantly attacked as one might think.
Robert E. Lee and the Army of Northern Virginia did have a plan to threaten the Union capital. Lee's overall strategy was to take the fight to the Union, rather than fight on Confederate soil. His advances north did threaten Washington, but Lee didn't attack DC directly. His best chance to hit the Union capital came after his surprising win at the first Battle of Bull Run (or First Manassas, for you Southerners). With the Union forces as stunned by their loss as the Confederates were stunned by their victory, the South was too disorganized to follow up. Once Washington realized the war was going to last much longer than anticipated, the District became one of the most fortified cities on Earth.
To make it more difficult for the Confederates to swing around and even conduct so much as a raid on Washington, Union Generals George G. Meade and Joseph Hooker kept their armies between the Confederates and Washington as Lee's army advanced north toward Gettysburg in 1863.
(American Battlefield Trust)
As for the city itself, the Potomac acted as a formidable natural barrier but it wasn't the only barrier. The city had a series of some 68 fortifications, 93 gun positions just waiting for cannon, 20 miles of trenches and 30 miles of military-use roads. It also 87 mounted guns and and 93 mortar positions and untold communications lines. These fortifications ringed the city, even in the Virginia areas. As much as the South would have liked to capture the District, it would have needed and army far beyond its capability. Still, there was one attempt.
In 1864, Confederate Gen. Jubal Early went north through the Shenandoah Valley while Lee's army was under siege at Petersburg, Va. Early forces relieved Lee's supply lines at Lynchburg before swinging north through the valley. He captured and ransomed Fredericksburg then moved on where he was met by a small Union defense force at Monocacy. Had it not been for this delaying action, Early might have taken Washington.
But giant cannons are kind of intimidating.
At this time the city was filled with refugees and troops of varying quality. Most of the battle-hardened Union troops were out in the field fighting the Confederates, so Washington's defenders weren't all the best of the best the Union could muster. The Confederate advance sent the city into a panic. Union General Lew Wallace didn't know if Baltimore or Washington was Early's target, but the citizens of both cities were freaking out, so Wallace knew he had to at least delay Early until reinforcements could arrive. The Marylanders held Early off for a full day at the cost of more than 1,200 lives. But it was enough to delay the advancing Confederates while inflicting some heavy casualties. Early rode on, though, and came across the northernmost fortification of Washington, Fort Stevens.
When he arrived, he had a strength roughly equal to that of the District's defenders. The defenders were mostly raw recruits and untested reservists, but combined with reinforcements, the city had a fighting chance. Going against the Confederate Army was the blazing heat of the July sun and the fact that they'd been on the march and fighting for nearly a month.The further delay allowed for more reinforcements by the Union defenders.
"Mr. President, maybe you could duck. Or at least take off your hat."
The attack began in the late afternoon on Jul. 11, 1864. Early's men began skirmishing with the Union fortification to test its defenses. As President Lincoln watched on, it began in earnest at 5 p.m. when veteran Confederate cavalry stormed the Union picket lines and Union artillery opened up on rebel positions across the lines. Over the coming night, more Union reinforcement would arrive and Early realized time was not on his side. Had he immediately attacked Fort Stevens, he might have taken the capital but waiting only allowed for more reinforcements and for the Union troops chasing him to catch up.
Early used skirmishers to cover his nighttime withdrawal. Fort Stevens and Washington's fortification had held but President Lincoln was almost hit by a bullet. Early was able to retreat back to the Army of Northern Virginia, where it's said he told Lee and his own staff officers, ""We didn't take Washington but we scared Abe Lincoln like Hell."