Complex sentence: The well has been known since at least the Roman period, and has been a site of pilgrimage since about 660 when Saint Winefride was beheaded there by Caradog who attempted to attack her.
Split into simpler sentences: The well has been known since at least the Roman period. It has been a site of Christian pilgrimage since about 660, dedicated to Saint Winefride who, according to legend, was beheaded there by Caradog who attempted to attack her.