The Trajaneum, situated at the highest point of the acropolis, is the only Roman monument on the upper fortress.
In the first building phase, the temple was surrounded by walls which were taken down by Hadrian to erect side halls whose capitals and entablature correspond to the older north hall. As the measurements of the former columns had been kept, the new columns, too low, had to be placed on short shaft parts with integrated bases. The upper two thirds of the side hall columns were fluted in order to increase the height by an optical effect. Statues were erected facing the temple on the pedestals standing between the columns.The north hall was connected to a row of old rooms located behind it. Because of their wall paintings, they were called "hellenistics chambers". The east hall ends in an apse.
The construction of the temple was started under Trajan (98-117 AD) and completed under his successor Hadrian (117-138) who enlarged it. The temple, dedicated to the cult of both emperors and Zeus, was built on a high marble covered podium. On the slope of the hill, parallel supporting walls covered with barrel vaults, forming a passage way, were built in order to support the large platform in front of the temple. In the Middle Ages, the wall facing the valley was included in the Byzantine fortifications and restored several times. Parts of the substructures were used as cisterns.
Between 1976-1994, restoration works were carried out by the Istanbul Department of DAI (Deutsches Archaologisches Institut) in cooperation with Turkish specialists and architects, archaeologists, stonemasons and experts from the whole of Europe. New excavations also revealed previous constructions from the Hellenistic period such as terraced residential and trade buildings.
