From March 537 to March 538 Belisarius successfully defended Rome against the much larger army of Vitiges. He inflicted heavy casualties by launching many successful sorties. While the range of the horse archers Belisarius used has often been credited with the success of these raids in the terrain around Rome, this wouldn't make sense. Instead, it was the Gothic unpreparedness and the command expertise of Byzantine officers which made sure the Goths were unable to respond. When Vitiges tried to post units to prevent these raids, Belisarius sent out bigger units that encircled them; the Gothic officers proved unable to counter this. 18 days into the siege, the Goths launched an all-out assault, and Belisarius ordered a number of archers to shoot at the oxen pulling the siege equipment. As a result, the assault failed with heavy casualties. When the Goths retreated from a certain section of the wall, Belisarius launched an attack on their rear, inflicting extra casualties. However, when he tried to end the siege by sallying out with a large force, Vitiges used his numbers to absorb the attack and then to counter-attack, winning the battle. Regardless, Vitiges was losing the siege, so he decided to make one last attempt on the wall which ran along the Tiber, where the wall was much less formidable. He bribed men to give the guards drugged wine, but the plot was revealed and Belisarius had a traitor tortured and mutilated as a punishment. An armistice had been signed shortly before, but with both the Goths and the Byzantines openly breaking it, the war continued. By then Byzantine forces had captured Ariminum (Rimini) and approached Ravenna, so Vitiges was forced to retreat. The siege had lasted from March 537 to March 538.