Complex sentence: Achillius was metropolitan of Larissa in Thessaly, Greece, and is remembered primarily for his vehement defense of orthodoxy during the Council of Nicea and a miracle he performed in testimony against Arianism.
Split into simpler sentences: Achillius was metropolitan of Larissa in Thessaly, Greece. Achillius is mainly remembered for his vehement defense of orthodoxy during the Council of Nicea and a miracle he performed in testimony against Arianism.