There are many iconographies on the Supreme Pontiffs, from St. Peter to the present day. The set used in this timeline is the one highly valued and officially acknowledged by the Vatican. It is found in the naves of the Patriarchal Basilica of  St. Paul- Outside the Walls in Rome, Italy.  The reproductions in the Pope Chart* are from this collection.  The collection is made of medallions in mosaic; each one has the Pontiff’s name written in Latin and the period of his pontificate in Roman numbers.  This iconography was started by St. Leo the Great in 498 and historically updated in 1947.
Popes’ Mosaic Icons
St. Peter 
42-67
The first Pope
* Chart copies of the mosaics available at: www.popechart.com/history.htm; adapted here for teaching purposes.
The Patriarchal Basilica
of  St. Paul Outside the Walls,
Rome, Italy.
Interior of St. Paul’s Outside the Walls
Enlarged section of the Basilica
showing the mosaics
Diagram showing
the chronological
order of the mosaics
in the Basilica