Complex sentence: Its ceiling is covered with frescos dating from the early part of the 13th century which depict the Visitation and miracles performed by the Virgin Mary which were revealed during conservation work in the 1990s.
Split into simpler sentences: Its ceiling is covered with frescos dating from the early part of the 13th century which depict the Visitation and miracles performed by the Virgin Mary. These were revealed during conservation work in the 1990s.