In 2000 and 2001 the German Archaeological Institute in Rome (under the direction of M. Heinzelmann) investigated the so-called navalia and a temple, that had partly been excavated in the 19th century by P.E. and C.L. Visconti. The structure is situated between the so-called Palazzo Imperiale 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 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 metres high. The temple itself must have been c. 15-16 metres high and the highest point was c. 23 metres above the water-level. It opened towards the 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 inscription CIL XIV, 376, from the second half of the second century AD. It tells us that P. 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.
Heinzelmann adduces as arguments that the statue base is far too big for a single statue, and the position of the temple. 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.