Possible Clues:

• Start of a string of 13 Popes
• First pope to be called 'the Great'
• First of a string of 13 popes
• First pope in a baker's dozen
• 5th century Pope known as ''The Great''
• Pope of the 400s
• 'The Great' pope between Sixtus III and Hilarius
• He was succeeded by his archdeacon Hilarius
• First in a string of 13 Popes
• Pope, 440-461