Union General Ulysses S. Grant sought to capture Richmond, the Confederate capital, and saw lightly defended Petersburg as the key to it. After failing to take Richmond from the north, he surprised Robert E. Lee by attacking Petersburg from the south, aided by Union General Benjamin Butler's forces. Grant reached Petersburg's defenses on June 15th, 1864, but General P.G.T Beauregard, commanding the Confederates in Petersburg, held off Union attacks for the next two days and kept the city in Confederate hands. Beauregard shifted more of his troops from the Bermuda Hundred lines, rebuilt the defenses, and late on June 17th received reinforcements from Lee. When the fighting ended on June 18th, 1864, Lee still held Petersburg, the key to Richmond. Before this, from May 31 to June 12, 1864, Lee had defeated Grant at Cold Harbor, stalling Grant's attempt on Richmond.