The development of Cannon following the discovery of Gunpowder caused a revolution in siege warfare. Cannon forced the redesign of most fortifications because the straight, high walls surrounding most cities could be easily battered down by direct fire. This was the fate of the walls at Constantinople, which had held various besiegers at bay for over a thousand years. On the battlefield, Cannon assumed an important role, but were unable to dominate because of the development of firearms.