The Petersburg Courthouse, built between 1837 and 1839, was the official Confederate headquarters during the Siege of Petersburg. On April 20, 1861, local volunteers formed in its square to enlist. On June 9, 1864, its bell sounded the warning for the local militia to meet the advancing Union cavalry. During the Siege, soldiers from both sides could see the courthouse clock from the trenches and they set their timepieces by it. The clock tower was a favorite target of Union artillerists, who poured an estimated 20,000 shells into the city.