Complex sentence: The site originated as a Gallo-Roman cemetery, in late Roman times--the archeological remains still lie beneath the cathedral; the people buried there seem to have had a faith that was a mix of Christian and pre-Christian beliefs and practices.
Split into simpler sentences: The site originated as a Gallo-Roman cemetery, in late Roman times. The archeological remains still lie beneath the cathedral; the people buried there seem to have had a faith that was a mix of Christian and pre-Christian beliefs and practices.