The arena was excavated about 6 meters deep below the existing ground level and the spoil was then used as landfill to create the western side of the earthworks. The earthworks were supported on all sides by a continuous sustaining wall which followed the shape of the arena. Outside this wall a second containing wall was built with buttresses and blind arches to form the exterior of the building. The arena was surrounded by a parapet more than 2 meters high, originally painted with scenes of the hunt and contests.