From Helderberg Hilltowns of Albany County, NY

At the time of the American Civil War, Petersburg was the second largest city in Virginia, and the seventh-largest city in the Confederacy. Its 1860 population was 18,266, half of whom were black. Free blacks numbered 3,224 (one-third) and had been attracted to the city for the opportunities in industries and trades.[12] Petersburg's population had the highest percentage of free African Americans of any city in the Confederacy and the largest number of free blacks in the Mid-Atlantic. Many had settled on Pocahontas Island. Because of its significant past and prehistoric archaeological evidence, the Pocahontas Island Historic District is listed on the National Register of Historic Places. Ninety percent of the population are native Virginians, as most of their ancestors had been in the state since the 17th and 18th centuries.

When the Civil War began in 1861, Petersburg was strategic. The city provided several infantry companies and artillery units to the Confederate Army, along three troops of cavalry. In April 1861 more than 300 free Petersburg African Americans volunteered to work on the fortifications of Norfolk, Virginia under their own leader. Slaveholders also contributed the help of numerous non-free black men.

In 1864, Petersburg became a target during the Overland Campaign of Union General Ulysses S. Grant. The numerous railroads made Petersburg a lifeline for Richmond, the Confederate capital. The depot at Pocahontas Island, built for the Richmond & Petersburg rail line, was a transit point for Confederate troops and supplies.

Ruins of pre-war slave quarters on the Petersburg Battlefield Petersburg was the headquarters of the Confederate Army's Second Regiment of Engineers, whose members included Benjamin Morgan Harrod, a Harvard-trained civil engineer who later designed the water and sewer systems of his native New Orleans, Louisiana.

After his defeat at the Battle of Cold Harbor, Grant remained east of Richmond and moved south to Petersburg. Grant intended to cut the rail lines into Petersburg, stopping Richmond's supplies. On June 9, troops led by William F. "Baldy" Smith of the 18th Corps, attacked the Dimmock Line, a series of defensive breastworks constructed in 1861 and 1862 to protect Petersburg against the Army of the Potomac under General George McClellan during the Peninsula Campaign. The Confederate troops numbered only 2,000, but Smith and Winfield S. Hancock were hesitant to attack the fortified line. Confederate General P.G.T. Beauregard informed Lee that he was facing virtually the entire the Army of the Potomac with his few defenders at Petersburg. Lee arrived with the fabled Army of Northern Virginia, and the 292-day Siege of Petersburg began. Lee himself admitted that the South could not win a siege war.

The trench lines on the east of Petersburg were close together. A soldier in the 48th Pennsylvania, a coal miner in civilian life, remarked, "We could blow that battery into oblivion if we could dig a mine underneath it." Colonel Henry Pleasants, his division commander, liked the idea and forwarded it up the chain of command. Grant gave his approval. On July 30, the explosives in the tunnel were detonated. Due to botched Union leadership and arrival of Confederate General William Mahone, the Union forces suffered a disastrous defeat at the Battle of the Crater, suffering over 4,000 casualties. The battle was portrayed in the film Cold Mountain (2003). In early April 1865, Union troops finally managed to push their left flank to the railroad to Weldon, North Carolina and the Southside Railroad. With the loss of Petersburg's crucial lifelines, the Confederate forces had to retreat, ending the siege in a victory for the Union Army.

The fall of Petersburg meant that Richmond could no longer be defended, Lee attempted to lead his men south to join up with Confederate forces in North Carolina. Hopelessly outnumbered, he was surrounded and forced to surrendered at Appomattox Court House on April 9, 1865. Confederate General Ambrose P. (A.P.) Hill died on the last day the Confederates held the Petersburg trenches. Petersburg established a warfare precedent. During World War I the armies on both sides used trenches extensively in Europe (qv. Trench warfare).