Possible Clues:

• Canonized fifth-cen. pope
• Fifth-century pope
• Canonized fifth-century pope
• Fifth cen. pope called "The Great"
• Canonized pope known as "the Great"
• Canonized 5th-century pope
• Pope in Attila's time
• Florida University named for a pope
• 'Great' pope of the fifth century
• Canonized pope who persuaded Attila not to attack Rome