Complex sentence: Castlemartyr was known as "Leperstown" in ancient times because of the Leper House that is said to have existed near Ballyoughtera, itself said by Smith to have become a village of some note during the Middle Ages.
Split into simpler sentences: Castlemartyr was known as "Leperstown" in ancient times because of the Leper House that is said to have existed near Ballyoughtera. Ballyoughtera itself, is said by Smith to have become a village of some note during the Middle Ages.