deputy (vicarius) of Peter, having received his apostolic 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 Apostle, 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 fulfilled his duties (sermon 1). Thus, the office of the Roman bishop was grounded on the special relationship between Christ and Peter, a relationship that cannot be repeated per se; therefore, Leo depended on Peter's mediation, his assistance and his example in order to be able to adequately fulfill his role and exercise his authority as the Bishop of Rome, both in the city and beyond. Leo and Attila After the indecisive outcome of the Battle of Chalons in 451, Attila invaded Italy in 452, sacking cities such as Aquileia and heading for Rome. He allegedly demanded that the sister of the reigning Emperor Valentinian III be sent to him with a dowry. In response, the emperor sent three envoys to negotiate with Attila: Gennadius Avienus, one of the consuls of 450, Memmius Aemilius Trygetius, the former urban prefect, and Leo. Little is known of the specifics of the negotiations, as a result of which Attila withdrew. Most ancient and medieval historians celebrated Leo's actions, giving him all the credit for this successful embassy. According to Prosper of Aquitaine who was alive at the time of the event, Attila was so impressed by Leo that he withdrew. Another near-contemporary was the historian Priscus who records that Attila was dissuaded from attacking Rome by his own men because they feared he would share the fate of the Visigothic king Alaric, who died shortly after sacking the city in 410. Paul the Deacon, in the late 8th century, relates that an enormously huge man dressed in priestly robes and armed with a sword, visible only to Attila, threatened him and his army with death during his discourse with Leo, and this prompted Attila to submit to his request. Writing in the early 20th century, the religious skeptic John B. Bury remarked: The fact of the embassy cannot be doubted. The distinguished ambassadors visited the Hun's camp near the south shore of Lake Garda. It is also certain that Attila