Possible Clues:

• Pope after Sixtus III
• Earliest pope to receive the title 'the Great'
• First in a string of popes
• First of a string of 13
• Saint known as 'the Great'
• "Great" pope
• Fifth-century pope who was sainted
• Pope who persuaded Attila not to attack Rome
• First in a line of 13 popes
• Hilarius succeeded him in A.D. 461