Engineers dug six metres below the surface of the lake and a further four metres into the clay subsoil until an oval shaped ditch, fifty metres wide and two-hundred metres long was achieved. The ditch was then lined with brick and concrete facings. Two brick walls were built with concrete laid in between. Overall, the facings were three metres thick and six and a half metres high. The concrete was poured to what had been the level of the lakebed. The foundations were then built, consisting of four travertine stone tunnels and a series of concrete vaults that ran under what would be the arena and seating areas. The travertine blocks held in place by a bed of powdered travertine mortar was laid over the concrete acted as the initial supports for the seating
Engineers dug six metres below the surface of the lake and a further four metres into the clay subsoil until an oval shaped ditch, fifty metres wide and two-hundred metres long was achieved. The ditch was then lined with brick and concrete facings. Two brick walls were built with concrete laid in between. Overall, the facings were three metres thick and six and a half metres high. The concrete was poured to what had been the level of the lakebed. The foundations were then built, consisting of four travertine stone tunnels and a series of concrete vaults that ran under what would be the arena and seating areas. The travertine blocks held in place by a bed of powdered travertine mortar was laid over the concrete acted as the initial supports for the seating