 These measures, along with the fire from ballistas and onagers mounted on the city walls, frustrated the Romans and forced them to attempt costly direct assaults.The siege bogged down to a stalemate with the Romans unable to force their way into the city or keep their blockade tight enough to stop supplies reaching the defenders, and the Syracusans unable to force the Romans to withdraw.The Carthaginians realised the potential hindrance a continuing Syracusan defence could cause to the Roman war effort and attempted to relieve the city from the besiegers but were driven back.