Complex sentence: Pope Calixtus III issued a bull in 1456 encouraging the pilgrimage to the Lady of the Pillar, acknowledged the miracle of its foundation and the miracles that have manifested in the Spanish shrine.
Split into simpler sentences: Pope Calixtus III issued a bull in 1456 encouraging pilgrimage to the Lady of the Pillar. It acknowledged the miracle of its foundation and the miracles that had taken place in the Spanish shrine.