Tombstone of a Young Man Named Felix
(CIL VI.12691)

Epitaph in the wall of the porch of S. Giorgio in Velabro, Rome: 1998 photo.

Transcribed, restored and expanded:

1 5	Dis Manibus ? ATRIVS FELIX QVI VIXIT ANNIS XXVIII MENSibus X VXXOR SVA BENE Merenti

Translated:

To the Shades of the Dead
(here lies) . . . ? Atrius Felix
who lived
28 years 10 months
his wife to her well-deserving (husband).

"Here lies" is not strictly accurate. This man was a pagan and the inscription is small, so the odds are the stone marked not his body but his ashes.
Despite the inexpert cutting, there is an attempt to make the inscription symmetrical, so we're probably missing the initial of his first name, or just conceivably the first letter of his name; he was thus either say Lucius (Quintus, Marcus, etc.) Atrius — or Patrius (Satrius, etc.) Felix.
Date: Late imperial; look at the characteristic shape of the A on the last line and of the M's, influenced by Rustic Capitals or one of the cursive scripts (i.e., handwriting used in manuscripts). No earlier than 2c A.D., probably much later.