web site at New York University, the base of chief excavator Kenan Erim, says:
The reliefs of the two buildings had very different programs and used different designers and executing workshops. And, although there was no overriding unified program, the subjects of the reliefs are divided into distinct themes and categories of subjects according to the four registers made by the two levels in each building.
Of the reliefs from the North Building, which collapsed earlier and was cleared while the South Building was still in use, much less survives; but enough is preserved to reconstruct its broad program. The upper storey had imperial and allegorical subjects, while the lower storey carried a series of conquered peoples and places of the Roman empire, each treated as a single statuesque female personification standing on an inscribed base. The inscriptions record peoples from Spain in the furthest west to the Arabs and Judeans in the east. There were fifty such figures, and their designs were no doubt borrowed directly from a monument in Rome.
The South Building was never substantially cleared after its final collapse, and more than sixty of its reliefs survive. The upper‘ storey reliefs juxtaposed traditional Greek gods with Roman imperial scenes and figures of victory. The Roman emperors from Augustus to Nero are treated in a strikingly elevated, Hellenistic manner, designed to present them as part of a new enlarged Olympian pantheon -- an idea captured in the phrase of one of the inscriptions which dedicated the building "to the Olympian god-emperors" ( tois theois Sebastois Olympiois ). Several of these reliefs highlight the conquests of Claudius and the young Nero.
The lower storey reliefs featured a remarkable series of forty-five Greek mythological scenes. Many were arranged in broad groupings of familiar scenes of favorite figures, such as Herakles and Dionysos, but there was no single sequential mythological program. Towards the east end, however, as one approached the Temple, there was a greater concentration of sacrifice scenes and of Rome-related myths, such as those featuring Anchises and Aeneas. And here the design made explicit what is implied in the whole complex, the close connection between Greek myth-history in the lower level and the godlike Augustan regime in the upper storey. In spite of the wide range of styles and levels of execution between individual reliefs, it was perhaps this juxtaposition of Greek and Roman, of myth and history, moulded visually by style and iconography into a single continuum, that was the most striking effect of the complex viewed as a whole.