 The interior is better preserved; beneath the arena are subterranean passages like those in the amphitheatre at Puteoli.It is one of the largest in existence; the longer diameter is , the shorter , and the arena measures , the corresponding dimensions in the Colosseum at Rome being 188, 155, 85, 53 metres (615, 510, 279 and 174 ft).To the east are considerable remains of baths – a large octagonal building, an apse against which the church of Santa Maria delle Grazie is built, and several heaps of debris.