When the camera is panning to Hannibal in front of St. Ambrose in Primavera, it passes by two other mosaics.  One is St. Catald.  (He is never in full-focus, so the screen cap above was the best I could do).

I would think that the saint had no particular importance to Hannibal except that in the show’s “reproduction” of the Cappella Palatina, they have moved the mosaic of St. Catald near to St. Ambrose so that they can share the screen.

St. Catald was an Irish monk who became an archbishop in Taranto, Italy.  He is invoked for protection from plagues, droughts and storms.  wherever he went, people flocked to him because of his ability to heal and to resurrect.

This all seems pretty straight-forward and potentially uninteresting.  However…

As with St. Ambrose, St. Catald has a particular and peculiar connection to the Fullerverse, if not to Hannibal itself:  “The joy which [St. Catald’s] birth brought his parents was quickly turned to sadness, for a few hours after the child came into the world, his mother died.  However, we are told that the infant fingers of the babe, having by chance touched the lifeless corpse that lay beside it, life returned, and the young mother, whose loss was mourned, was restored to her husband and child.” (x)

(Yep!  St. Catald was the medieval Ned the Piemaker!)

from here and here