There used to be an optional course in Rome that everyone seemed to end up taking at one time or another: Fr Martinez-Fazio's course on paleo-Christian iconography. Complete with slides, it gave us an introduction to the many early Christian monuments that we would see on our visits to the catacombs and to other holy sites in Rome - such as San Lorenzo Fuori le Mura.
Here is a whale - recalling the story of Jonah and included on Christian monuments as a symbol of the resurrection:
Here is an image of the feeding of the 5,000 - calling to mind the Eucharist as the pledge of eternal life (Our Lord is second from the left):
On the next fragment there is a dove with an olive branch - a common symbol recalling the end of the flood and indicating Baptism. You can also see the very common Chi-Rho symbol (the first two letters of the Greek word "Christos")
One more: this has a list of virtues attributed to someone who died.
HAEC OMNIA TULIT SEC[um]
Faith (/faithfulness), chastity, truth, modesty, integrity - he bore all these in himself (or she... herself)
Rather more noble than "he liked a drink and a bet on the horses."