Roman concrete
The outer voussoirs of the arch rib are built of alternating bricks and ashlar stones, while the rest of the arch vaults consists entirely out of bricks. Further materials mentioned by Wiegand include marble – probably for facing – and mortar, which could have been used as a binder, or may refer to Roman concrete which often served to fill the interior of the spandrels and the piers. Ancient Spolia were reportedly not used.