Where did the king sit in the arena?
The King sits in the arena as well, but sits in a high position so as to be above the crowd and to be able to observe and judge all of the action, as well as the response from the people.
"When all the people had assembled in the galleries, and the king, surrounded by his court, sat high up on his throne of royal state on one side of the arena, he gave a signal, a door beneath him opened, and the accused subject stepped out into the amphitheater. Directly opposite him, on the other side of the inclosed space, were two doors, exactly alike and side by side." (Stockton)