Petersburg, Virginia, was a vital rail center that brought critical supplies to nearby Richmond, the capital of The Confederacy. Union General Ulysses Grant knew that if Petersburg fell, Richmond would be right behind it. Grant had spent May in a series of series of largely inconclusive battles fighting alongside General George G. Meade’s Army of the Potomac—including the Battle of Cold Harbor on May 31, where both sides sustained heavy losses.

In June 1864, Grant marched his army around the Army of Northern Virginia, crossed the James River and advanced his forces to Petersburg.

Lee raced to reinforce the Petersburg’s defenses. On June 15, 1864, the Battle of Petersburg began when General William F. Smith moved his 10,000 Union troops against the Confederate defenders, a few thousand armed old men and boys commanded by General P.G.T. Beauregard. Despite their smaller numbers, the Confederate city’s physical defenses held.

Federal troops arrived the next day, and Beauregard received reinforcements from General Robert E. Lee. The Confederate line held fast despite several Union attacks.

By June 18, 1864, Grant had nearly 100,000 men under him at Petersburg. The 20,000 Confederate defenders held on, awaiting reinforcements from the rest of Lee’s Army of Northern Virginia. Grant realized the fortifications erected around the city would be difficult to attack and pivoted to starving out the entrenched Confederates.

READ MORE: American Civil War: Causes and Dates

The Siege of Petersburg was marked by the brutal and elongated use of trench warfare. The front would eventually stretch for almost 40 miles and claim 70,000 casualties over the next ten months.

The first trenches were dug back in 1862, long before the siege. Engineer Charles Dimmock had designed a ten-mile trench line around Petersburg in a "U" shape, anchoring on the southern bank of the Appomattox. There were 55 gun batteries and walls as high as forty feet in certain areas.

Throughout the long winter, Confederate soldiers hunkered down within the fortified walls of the city. With Southern railroads and their supply lines severely damaged, Confederate troops suffered from hunger and exhaustion. Many deserted.

On March 24, 1865, President Abraham Lincoln, First Lady Mary Todd Lincoln, and their son, Tad, traveled to General Grant’s headquarters in City Point, Virginia. (Grant employed Lincoln’s son, Robert Todd Lincoln, on his staff). While there, Lincoln witnessed Lee make a desperate attack on Union lines at the Battle of Fort Stedman on March 25. Grant began preparing for a major offensive.

Grant and Lincoln were soon joined by William Tecumseh Sherman, who was fresh off his “March to the Sea” from Atlanta to Savannah. He traveled nearly 100 miles to the North Carolina coast, then took a captured Confederate blockade runner to City Point. The three men met on board Lincoln’s steamship, the River Queen, for two days in a row. It was to be the only meeting between Grant, Lincoln, and Sherman, and the three plotted out strategy for the final days of the Civil War.

The Union Army earned a hard-won victory after months of fighting. Grant’s big attack came at Five Forks on April 1, where he crushed the end of Lee’s line southwest of Petersburg. His victory was followed by a second win for the Union Army on April 2, 1865, when General Phillip Sheridan assaulted Lee’s depleted right flank. Grant ordered an attack on all fronts and the Army of Northern Virginia began to retreat.

Less than a week later, Grant’s massive army headed off the remnants of the Army of Northern Virginia at Appomattox Station. With Confederate forces cut off from provisions and support, Lee famously said, “there is nothing left me to do but to go and see Gen. Grant, and I would rather die a thousand deaths.”

On the evening of April 2, the Confederate government fled Richmond, followed by the army. Union troops entered a conquered Richmond on April 3, 1865 after ten months of campaigning. Lincoln greeted freed slaves in the streets. The Confederate capital was finally in Union hands.

On April 9, 1865, near the town of Appomattox Court House, Virginia, Confederate General Robert E. Lee surrendered his Army of Northern Virginia to Union General Ulysses S. Grant.

Grant told his officers, “The war is over. The Rebels are our countrymen again.” Although scattered resistance continued for several weeks—the final skirmish of the Civil War occurred on May 12 and 13 at the Battle of Palmito Ranch near Brownsville, Texas—for all practical purposes the Civil War had come to an end.