, ▁was ▁Bishop ▁of ▁Rome ▁from ▁ 2 9 ▁September ▁ 4 4 0 ▁and ▁died ▁in ▁ 4 6 1 . ▁Pope ▁Bened ict ▁XVI ▁said ▁that ▁Leo ' s ▁pap acy ▁"... was ▁und ou bt edly ▁one ▁of ▁the ▁most ▁important ▁in ▁the ▁Church ' s ▁history ." ▁ ▁He ▁was ▁a ▁Roman ▁arist ocrat , ▁and ▁was ▁the ▁first ▁po pe ▁to ▁have ▁been ▁called ▁" the ▁Great ". ▁He ▁is ▁perhaps ▁best ▁known ▁for ▁having ▁met ▁Att ila ▁the ▁Hun ▁in ▁ 4 5 2 ▁and ▁alleg edly ▁persu aded ▁him ▁to ▁turn ▁back ▁from ▁his ▁invasion ▁of ▁Italy . ▁He ▁is ▁also ▁a ▁Doctor ▁of ▁the ▁Church , ▁most ▁remembered ▁the olog ically ▁for ▁issu ing ▁the ▁T ome ▁of ▁Leo , ▁a ▁document ▁which ▁was ▁a ▁major ▁foundation ▁to ▁the ▁deb ates ▁of ▁the ▁E c umen ical ▁Council ▁of ▁Chal ced on . ▁The ▁Council ▁of ▁Chal ced on , ▁the ▁fourth ▁ec umen ical ▁council , ▁de alt ▁primarily ▁with ▁Christ ology , ▁and ▁el uc id ated ▁the ▁orth odox ▁definition ▁of ▁Christ ' s ▁being ▁as ▁the ▁hyp ost atic ▁union ▁of ▁two ▁n atures , ▁divine ▁and ▁human , ▁un ited ▁in ▁one ▁person , ▁" with ▁neither ▁confusion ▁nor ▁division ". ▁It ▁was ▁followed ▁by ▁a ▁major ▁sch ism ▁associated ▁with ▁Mon oph ys it ism , ▁M ia phys it ism ▁and ▁Dy oph ys it ism . ▁ ▁Early ▁life ▁ ▁According ▁to ▁the ▁Liber ▁Pont ific alis