Complex sentence: Then on to Thebes and Corinth, and finally down into the Peloponnese, particularly into Sparta, which he reputably saved from a plague and where he built three churches and a monastery continuing his preaching and teachings, which were reportedly confirmed by miracles.
Split into simpler sentences: Then on to Thebes and Corinth, and finally down into the Peloponnese, particularly to Sparta, which he reputably saved from a plague. There he also built three churches and a monastery continuing his preaching and teachings, which were reportedly confirmed by miracles.