I corrected the perspective of this picture. The picture can be seen to the left of the arch above the entrance.

As for what it depicts: a researcher informed me, this is Saint Gregory the illuminator being tortured...again! He's got iron chains on his feet that make him bleed everytime he moves. He is being dragged and pushed by the employees of king Trad III who wants him dead. Later, the king will convert to Christianity, when he realizes the sanctity of Gregory.