Complex sentence: The institute also has one of the world largest coin collections-especially of Roman and Byzantine coins-which was supplemented in 1967 with 15,000 coins from Phillip Whitting and Geoffrey Haines.
Split into simpler sentences: The institute also has one of the world's largest coin collections, especially of Roman and Byzantine coins. This outstanding collection was supplemented in 1967 with 15,000 coins from Phillip Whitting and Geoffrey Haines.