Complex sentence: During his papacy Peter II was obliged for a while to seek refuge to Rome from the persecuting Arians, he was received by Pope Damasus I; who sympathised with him and gave him support against the Arians.
Split into simpler sentences: During his papacy Peter II was obliged for a while to seek refuge to Rome from the persecuting Arians. He was received by Pope Damasus I, who sympathised with him and gave him support against the Arians.