Complex sentence: There is also a locally held belief that Mary, the mother of Jesus is buried in the village although why Mary should have found herself at the outer edges of the Roman empire at such a fraught time in the history of Anglesey is unknown.
Split into simpler sentences: There is also a locally held belief that Mary, the mother of Jesus is buried in the village. However, why or how Mary should have found herself at the outer edges of the Roman empire at such a fraught time in the history of Anglesey is unknown.