Nor was Placidia herself slow to add to the ecclesiastical splendour of her city. We have already seen that she built S. Giovanni Evangelista, rebuilt in the thirteenth century, in fulfilment of her vow and in memory of her salvation from shipwreck. Close to her palace she built another church in honour of the Holy Cross, and attached to it she erected her mausoleum, which remains perhaps the most precious monument in the city. The church and the monastery which her niece Singleida built beside it have perished. But though during the lifetime of Placidia Italy was free from foreign invasion, the decay of the western empire, of what had been the western empire, was by no means arrested; on the contrary, Britain, Gaul, Spain, and Africa were finally lost. Two appalling catastrophes mark her reign, the Vandal invasion of the province of Africa and the ever growing cloud of Huns upon the north-eastern frontiers. [Illustration: THE APSE OF S. GIOVANNI EVANGELISTA] Placidia's two chief ministers were Boniface and Aetius, either of whom, according to Procopius, "had the other not been his contemporary, might truly have been called the last of the Romans." Their simultaneous appearance, however, finally destroyed all hope of an immediate resurrection of civilisation in the West. For Boniface, whose "one great object was the deliverance of Africa from all sorts of barbarians," betrayed Africa to the Vandals, and to this he was led by the rivalry and intrigue of Aetius who, on the other hand, must always be remembered for his heroic and glorious victory over Attila at Chalons which delivered Gaul from the worst deluge of all--that of the Huns.