Complex sentence: The first chapel in the town (now the Church of St. Thomas Becket) was originally built by the Normans but was replaced with a larger building a hundred years later, and is now almost entirely of 18th-century construction.
Split into simpler sentences: The first chapel in the town (now the Church of St. Thomas Becket) was originally built by the Normans but was replaced with a larger building a hundred years later. The current building is now almost entirely of 18th-century construction.