Moreover, the desertions of allied Indian troops made ineffective the British defence of Fort William, which fell to the siege of Bengali forces on 20 June 1756. The surviving defenders who were captured and made prisoners of war numbered between 64 and 69, along with an unknown number of Anglo-Indian soldiers and civilians who earlier had been sheltered in Fort William.[citation needed] The English officers and merchants based in Kolkata were rounded up by the forces loyal to Siraj ud-Daulah and forced into a dungeon known as the "Black Hole".