Taken from Reddit, since my own Latin is nonexistent:
Liccai, member of Breuci Celtic tribe regarding his honorable discharge from the Roman army. Both tiles and five wax seals of witnesses have been preserved. The holder of the diploma is Centurion Liccai, son of Birsa from Marsunnia, a veteran of the Misena fleet.
I can't find a direct translation online anywhere, but that seems to sum it up.
PugJesus