I am very happy that you spotted the cannon ball mistake. In fact, it was a projectile from a ballista. As for the coin, it was a barbaric imitation of a coin of Constantine I. According to most publications, it was issued in the 380s AD by a mint in the area occupied then by the Goths. Close to this coin, a late Roman arrowhead was found. These were surface finds a few meters from the excavated house that was burned down and the ballista projectile was recovered from its interior. (a member of the Tenea Project Team)