Alexander : a history of the origin and growth of the art of war from ...

SHEDS AND MOUNDS. 173side this a wall of circumvallation at a suitable distance andfacing outward to prevent a relievingwith the operations of the besiegers.army from interferingIn front of the wall of contravallation mounds were erected,from which the walls ofthe town could be attacked.These were graduallythrown up underthe protection of movablescreens or sheds, or,as they also were sometimescalled, tortoises.One common form ofshed was a roof built ofand sustained by heavybeams, covered with clayor tiles and fresh skinsand other materials calculatedto resist fire, andTortoise.mounted on wheels. Two lines of sheds were sometimesbuilt on a slightly converging angle up to a certain distancefrom the wall, and then the lines united. The front of thesesheds towards the enemy was protected by hanging on themblankets made of rawhides and twisted ropes.The mound itself was constructed of earth, stones, trees,sometimes trestlework, the whole filled in with earth andstones or any material which could be quickest got togetherand would bear the weight of the towers which were to beadvanced. The mound had a gradual slant upwards towardsthe wall, but as erect a face as possible at the ditch. Uponor beside this mound, during erection, smaller towers wereplaced from which the besiegers could be attacked witharrows, darts and stones, and prevented from interrupting the