Complex sentence: The next day, the two canons were taken to Santa Cecilia in Trastevere to choose amongst the many relics there, and there they saw a skull shining brightly, the skull of Saint Lucius.
Split into simpler sentences: The next day, the two canons were taken to Santa Cecilia in Trastevere to choose amongst the many relics there. They saw a skull shining brightly, the skull of Saint Lucius.