RTF is a global modification that replaces all towns in the game.

you'll need to focus on the buildings; you can place several berserker buildings around the arena, creating a kind of plaza with human buildings. Alternatively, you can move the houses behind the fortress wall, near the shipyard (those above level 150 aren't allowed in the city).
The arena can be repurposed into other buildings; you can add a cage-dome and populate it with animals, or pile up stones and place a golem in the center – as a place where they are revived and assembled. There are many options, but you can also add a cage to the Thane's house.