▁so ▁as ▁a ▁means ▁of ▁maintain ing ▁unity ▁among ▁the ▁churches . ▁▁ ▁Besides ▁rec ourse ▁to ▁bib lic al ▁language , ▁Leo ▁also ▁described ▁his ▁own ▁special ▁relationship ▁with ▁Peter ▁in ▁terms ▁derived ▁from ▁Roman ▁law . ▁He ▁called ▁himself ▁the ▁( un worth y ) ▁he ir ▁and ▁deput y ▁( vic arius ) ▁of ▁Peter , ▁having ▁received ▁his ▁apost ol ic ▁authority ▁and ▁being ▁obliged ▁to ▁follow ▁his ▁example . ▁On ▁the ▁one ▁hand , ▁Peter ▁stood ▁before ▁him ▁with ▁a ▁claim ▁on ▁how ▁Leo ▁is ▁to ▁exercise ▁his ▁office ; ▁on ▁the ▁other ▁hand , ▁Leo , ▁as ▁the ▁Roman ▁bishop , ▁represented ▁the ▁Apost le , ▁whose ▁authority ▁he ▁held . ▁Christ , ▁however , ▁always ▁comes ▁out ▁as ▁the ▁source ▁of ▁all ▁grace ▁and ▁authority , ▁and ▁Leo ▁is ▁responsible ▁to ▁him ▁for ▁how ▁he ▁ful filled ▁his ▁duties ▁( ser mon ▁ 1 ). ▁Thus , ▁the ▁office ▁of ▁the ▁Roman ▁bishop , ▁was ▁ground ed ▁on ▁the ▁special ▁relationship ▁between ▁Christ ▁and ▁Peter , ▁a ▁relationship ▁that ▁cannot ▁be ▁repeated ▁per ▁se ; ▁therefore , ▁Leo ▁dep ended ▁on ▁Peter ' s ▁med iation , ▁his ▁assistance ▁and ▁his ▁example ▁in ▁order ▁to ▁be ▁able ▁to ▁ade qu ately ▁ful fill ▁his ▁role ▁and ▁exercise ▁his ▁authority ▁as ▁the ▁Bishop ▁of ▁Rome , ▁both ▁in ▁the ▁city ▁and ▁beyond . ▁ ▁Leo ▁and ▁Att ila ▁▁ ▁Despite ▁his ▁defeat ▁at ▁the ▁Battle ▁of ▁Chal ons ▁in ▁ 4 5 1 , ▁Att ila ▁inv