Possible Clues:

• Fifth-century pope known as 'the Great'
• First pope to be called 'the Great'
• First in a string of popes
• Pope of the 400s
• Pope who persuaded Attila not to attack Rome
• Fifth-century pope who was sainted
• Saint known as 'the Great'
• First pope in a baker's dozen
• 5th century Pope known as ''The Great''
• First of a string of 13