Complex sentence: None of the original church built by Llywelyn in Trefriw remains, except possibly for part of the wall of the South aisle, the result of heavy remodelling in the 15th and 16th centuries, and again in the 19th century.
Split into simpler sentences: None of the original church built by Llywelyn in Trefriw remains, except perhaps for small parts of the walls. It was rebuilt in the 15th and 16th centuries, and again in the 19th century.