It is important to remember that the Parthenon was in use over several centuries and that it was adapted through time. In this north-east corner of the pediment is the (replica) of one of the horses of Selene, and at the south-east corner Helios emerging.
Below the pediment is a series of metopes showing a gigantomachy. (This theme was developed by the later Attalid sculptures, dated after 200 BC, placed in front of the east end of the Parthenon.)
The north-east corner of the Parthenon was later obscured by the construction of the Attalid monument, surmounted by a bronze chariot, for Attalos II, c. 178 BC. His chariot made the visual connection with the chariot containing Selene.
On the architrave below each metope is a hole with the shadow of a circle. These are where the 14 gilded shields from Alexander the Great’s victory at Granikos (334 BC) were mounted. Thus Alexander was making the point that his victory over the Persians was as heroic as the gigantomachy.
Between each of the shields, and immediately below the triglyphs, are a series of holes. These are the traces of a bronze inscription that was pegged onto the architrave during the reign of the Roman emperor Nero in AD 61/2. This text honoured Nero, and it was erected by Tiberius Claudius Novius. They may have reflected Nero’s campaigns against the ‘new’ Persians, in the areas of Armenia and Parthia. In this way the dedication picked up the original 5th century BC Athenian iconography that celebrated the Hellenic victories over the Persians at Salamis and Plataia.