After all the preparations were made, an advance was ordered from the two rivers for assault at the main point, where the _tumler_ was already at work. The principal feature of this machine was a huge tree-trunk, a hundred feet in length, suspended by chains. It was drawn back by hand and then propelled against the wall with terrific force. At the head of it was a sickle-shaped iron, for tearing away dislodged stones. As the _tumler_ could only be used in the immediate vicinity of the enemy, its operators were protected by a low building called “the cat.” It had strong sides and a roof to which the chains were attached. The whole rested upon wooden block wheels by which it could be pushed up to the walls.