Complex sentence: The Rotonda is the oldest of Thessaloniki's churches, and some publications in Greece claim that it is the oldest Christian church in the world, although there are a number of other claimants to that title.
Split into simpler sentences: The Rotonda is the oldest of Thessaloniki's churches, and some publications in Greece claim that it is the oldest Christian church in the world. There are a number of other claimants to that title.