Complex sentence: During his travels he built up a collection of gems, reliefs, paintings, sculpture and reliefs, losing the paintings when the collection was interned in Portugal during his return trip from the east to England via Rome in 1787--88.
Split into simpler sentences: During his travels he built up a collection of gems, reliefs, paintings, sculpture and reliefs. He lost the paintings when the collection was interned in Portugal during his return from the east to Britain via Rome in 1787--88.