Richmond, Virginia:

Three years later, as March 1865 ended, the Confederate capitol became indefensible. On March 25, Confederate General John B. Gordon's desperate attack on Fort Stedman east of Petersburg failed. On April 1, General Philip Sheridan, assigned to interdict the Southside Railroad, met brigades commanded by George Pickett at the Five Forks junction, smashing them, taking thousands of prisoners, and encouraging General Grant to order a general advance. When the Union Sixth Corps broke through Confederate lines on Boydton Plank Road south of Petersburg, Confederate casualties exceeded 5000, or about a tenth of Lee's defending army. General Lee then informed Jefferson Davis that he was about to evacuate Richmond.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". In what month of 1865 was Richmond judged to be no longer able to be defended?
March