Besides the ram and the testudo, with which every boy becomes acquainted in the plates to his _Roman Antiquities_, there were the instruments bearing the quadrupedal names of the war-wolf, the cat, and the sow. “The cattus or cat-house, gattus or cat,” says the instructive Grose, “was a covered shed, occasionally fixed on wheels, and used for covering of soldiers employed in filling up the ditch, preparing the way for the movable tower, or mining the wall. It was called a cat because under it soldiers lay in watch like a cat for its prey. Some of these cats had crenelles and chinks, from whence the archers could discharge their arrows. These were called castellated cats. Sometimes under this machine the besiegers worked a small kind of ram.”[22] The sow reminds all true Scotsmen of Black Agnes of Dunbar jeering Salisbury with the farrowing of his sow, when she toppled on its wooden roof a mass of rock, and beheld the mutilated sappers crawling from beneath their shattered protector, like so many pigs. But the chief of all besieging works was the movable tower, brought up face to face with the defenders, and containing battering-rams below, with the various instruments already mentioned, employed in its several upper storeys. To oppose such a formidable engine, which could only be applied by some commander of vast resources, the flanking round towers were of invaluable service, as the bastions and outworks are at the present day. The main difference in the projectile direction of the operations in the two is, that while the fire of a fort is chiefly horizontal, the assaults made by the Norman keep were vertical, and hence came the crest of machicolations and turrets which has given so picturesque a character to the whole school of baronial architecture. The instances of the Norman castle in its more perfect shape, still existing, are very interesting in a historical view. It may be observed, that in the settled districts of England there are specimens of the older and ruder style of Norman work; but that, in the Edwardian conquests, the fully developed form is the oldest of which vestiges are to be found.