What was the longest siege of the American Civil War, lasting nearly ten months?

The longest siege of the American Civil War, lasting nearly ten months, was the Siege of Petersburg. It began in June 1864 when Union forces under Ulysses S. Grant tried to seize Petersburg, Virginia, a vital rail hub supplying the Confederate capital of Richmond. Rather than falling quickly, the city became the center of an extensive trench system.

The fighting continued from June 9, 1864, until April 2, 1865, although historians often describe the central period as a ten-month siege. Union troops repeatedly extended their lines westward, cutting Confederate rail connections and gradually tightening the pressure on Robert E. Lee's Army of Northern Virginia.

Petersburg was not one continuous assault but a campaign of battles, artillery exchanges, raids, and trench warfare. The famous Battle of the Crater, on July 30, 1864, followed a Union attempt to explode a mine beneath Confederate defenses, but the attack failed disastrously.

The Confederate defeat at Five Forks on April 1, 1865, made Petersburg untenable. Lee evacuated both Petersburg and Richmond shortly afterward, beginning the retreat that ended with his surrender at Appomattox Court House on April 9.