Complex sentence: During penal times, mass was said in the structure in the graveyard and over the altar is an aperture through which a warning could be communicated to the priest from a watcher positioned on the motte.
Split into simpler sentences: During penal times, mass was said in the structure in the graveyard. Over the altar is an aperture through which a warning could be communicated to the priest from a watcher positioned on the motte.