Complex sentence: His successor, Abbot John, founded on the eastern shore of the Bosphorus, opposite Sostenium or Istenia, the Irenaion, always referred to in ancient documents as the "great monastery", or motherhouse of the Acoemetae.
Split into simpler sentences: His successor, Abbot John, founded the Irenaion, on the eastern shore of the Bosphorus, opposite Sostenium or Istenia. In ancient documents it was referred to as the "great monastery", or motherhouse of the Acoemetae.