Roman siege engines were, for the most part, adapted from Hellenistic siege technology. Relatively small efforts were made to develop the technology; however, the Romans brought an unrelentingly aggressive style to siege warfare that brought them repeated success. Up to the first century BC, the Romans utilized siege weapons only as required and relied for the most part on ladders, towers and rams to assault a fortified town. Ballistae were also employed, but held no permanent place within a legion's roster, until later in the republic, and were used sparingly. Julius Caesar took great interest in the integration of advanced siege engines, organizing their use for optimal battlefield efficiency. Army engineering corps To facilitate this organization and the army's self-sufficiency, an engineering corps was developed. An officer of engineers, or praefectus fabrum, is referenced in armies of the late republic, but this post is not verifiable in all accounts and may have simply been a military advisor on the personal staff of a commanding officer. There were legion architects (whose rank is yet unknown) who were responsible for the construction of war machines who would also assure that all artillery constructions in the field were level. Ensuring that constructions were level was the job of the libratores, who would also launch missiles and other projectiles (on occasion) during battle (Le Bohec 1994: 52). The engineering corps was in charge of massive production, frequently prefabricating artillery and siege equipment to facilitate its transportation. Artillery Roman artillery was very efficient at that time, and during a siege the Romans would attack the weakest area of their enemy's defenses and attempt to breach the walls at that point. To support this effort, artillery fire would commence, with three main objectives: to cause damage to defenses, casualties among the opposing army, and loss of enemy morale. It would also provide cover fire for troops building siege ramps or those in siege towers. There were machines called tormenta , which would launch (sometimes incendiary) projectiles such as javelins, arrows, rocks, or beams. These devices were on wheeled platforms to follow the line's advance. All were "predicated on a principle of physics: a lever was inserted into a skein of twisted horsehair to increase torsion, and when the arm was released, a considerable amount of energy was thus freed". It was later stated that sinew, instead of twisted hair, provided a better “spring.” These weapons were