This isn’t a Lego Colosseum but only a ring of bricks. And it is characterised for Medieval times. In spite of all, I think that this could be a beautiful arena. Only the fact that Lego bricks are rectangular, and these ones create a ring, fascinates me. Well, it is something among a circular fortress, a fighting pit and an arena. It could become an amphitheatre with some little modifications. I found it here.