Demetrius being extremely mortified to see all his batteries on the side of the harbour rendered ineffectual, resolved to employ them by land, in order to carry the place by assault, or reduce it to the necessity of capitulating. He therefore prepared materials of every kind, and formed a machine called _helepolis_, which was larger than any that had ever been invented before. The basis on which it stood was square, and each of its sides was seventy-five feet wide. The machine itself was an assemblage of large square beams, riveted together with iron; and the whole mass rested upon eight wheels, that were made proportionable with the superstructure. The felloes of the wheels were three feet thick, and were strengthened with large iron plates. In order to facilitate and vary the movements of the helepolis, castors were placed under it, so that it could be moved in any direction. From each of the four angles a large column of wood was carried up to the height of about one hundred and fifty feet, inclining towards each other. The machine was composed of nine stories, whose dimensions gradually lessened in the ascent. The first story was supported by forty-three beams, and the last by no more than nine. Three sides of the machine were plated over with iron, to prevent its being damaged by the fires launched against it from the city. In the front of each story were little windows, whose form and dimensions corresponded with the nature of the arrows that were to be shot from the machine. Over each window was a kind of curtain made of leather, stuffed with wool: this was let down by a machine; and the intention of it was to break the violence of whatever might be discharged against it. Each story had two large staircases, one for the ascent of the men, and the other for their descent. This machine was moved forward by three thousand four hundred of the most powerful men in the army; but the art with which it was built greatly facilitated the motion. Demetrius likewise gave directions for the building of a great number of other machines, of different magnitudes and for various purposes; he also employed his seamen in levelling the ground over which his machines had to move, which was a hundred fathoms in length. The number of artisans and labourers employed on these works amounted to nearly thirty thousand men, which enabled them to be completed with astonishing rapidity. The Rhodians were not indolent during these formidable preparations, but employed their time in raising a counter wall on the tract of ground where Demetrius intended to batter the walls of the city with the helepolis; and for this purpose they demolished the wall which surrounded the theatre, as also several neighbouring houses, and even some temples, having solemnly promised the gods to build magnificent structures for the celebration of their worship after the siege should be raised.