In 2000 and 2001 the German Archaeological Institute in Rome, under the direction of Michael Heinzelmann, investigated the so-called navalia (shipyard) and a temple, which had partly been excavated in the 19th century by P.E. and C.L. Visconti. The structure is situated between the so-called Imperial Palace and a newly discovered harbour basin. It consists of a huge platform (c. 70 x 65 metres; opus mixtum), below which are deep, rectangular rooms and on top of which was a temple.
The west part of region I. The navalia and temple, indicated in red, are at nrs. 33 and 21 (trenches).
Plan: Michael Heinzelmann.The rooms below the platform are situated on the north and west side, oriented north-south and west-east respectively. They were accessed from the Tiber and the harbour basin, and filled with water. They were covered by barrel vaults. The northern rooms are c. 30 metres deep and 5.20 wide. In the western rooms sloping ramps were found and they were apparently drydocks or slipways. On the east side of the platform are shops, behind a porticus of large tufa arches.
Plan of the navalia and temple (Michael Heinzelmann).The terrace above the rooms was covered with opus spicatum. Numerous marble fragments of the decoration of a podium-temple were found here. The podium measured 19.50 x 9.50 and was c. 2 meters high. The temple itself must have been c. 15-16 meters high and the highest point was c. 23 meters above the water-level. It was facing west, that is, towards the mouth of the Tiber. The facade had four columns with a diameter of c. 1.05. The cella measured 9.20 x 7.40. Its walls consisted entirely of marble blocks. Against the back wall was a statue base (3.50 x 3.20). The open space in front of the temple was flanked by two large apses and a porticus. There was also a porticus behind the temple.
Reconstruction drawing of the navalia and temple, behind the newly discovered harbour basin.
From the north-west. Drawing: Michael Heinzelmann.The structure seems to have been built during the reign of Tiberius or Claudius. It was restored in the Severan period. According to Heinzelmann it is mentioned in an inscription from the second half of the second century AD (CIL XIV, 376). It tells us that Publius Lucilius Gamala aedem Castoris et Pollucis rest(ituit) and navale a L. Coilio aedificatum extru[e]ntibus fere collapsum restituit: he restored a temple of the Dioscures and docks (navale) built by Lucius Coilius, that were in a ruinous state. This Coilius may have lived in the first half of the second century BC. Gamala's work has not been traced in the few trenches that were dug.
For the identification of the temple Heinzelmann adduces as arguments the position of the temple, and the size of the statue base in the cella, far too big for a single statue. The Dioscures were in Ostia worshipped as protectors of shipping. From ancient texts we know that games were held at Ostia on 27 January. The festivities were led by the praetor urbanus, later by the praefectus urbis or a consul, which is documented as late as 359 AD. In the temple oracles were given. Heinzelmann suggests that the ships should protect the Tiber mouth, but that seems strange in the Imperial period.
