The Imperial Palace is said by Malalas to have begun construction under Gallienus (253-268AD) the complex was filled out by Diocletian. However when one goes back to accounts of the earthquake of 115 AD, Dio Cassius relates that "Trajan made his way out through a window of the room in which he was staying. Some being, of greater than human stature, had come to him and led him forth, so that he escaped with only a few slight injuries; and as the shocks continued over several days, he lived out of doors in the hippodrome". The hippodrome adjoins the Imperial Palace so there must have been some structure there at the time.
Above we show an excerpt from the map of Downey. It would be fairly reasonable to expect that the palace connected to the hippodrome in the form of an Imperial box. This may have been by having the palace directly abut the sporting structure or a bridge across a street. The Palatine palace complex in Rome was contiguous with the Circus Maximus and the palace of Galerius at Thessalonica also had this feature of close proximity.
The style of the Antioch palace was probably in the tradition of the late Empire palaces such as that of Diocletian at Split (shown below) and Galerius at Thessalonica. This would make sense. Note the columned arcade at the top of the sea wall. The pillared section of the Antioch Palace, as mentioned later in Libanius, may have been somewhat similar.
Both of these palaces had a similar principal in the form of a enormous rectangle divided into four quadrants by arcaded passageways that then met in the middle where there was a polygonal structure (usually octagonal). The octagonal structure is important to mention as it may have had its Antioch equivalent in a dramatically larger version, the famed Golden Octagon of Constantius, which we shall dwell upon in another posting.
Below we have the plan of the Palace at Split. This was 192 metres by 158 metres. Some comments have the palace at Antioch being 500 metres long on its main facade. So it would have been a dramatically scaled up version from that at Split.
It is not unreasonable that the palace in Antioch could have been substantially larger than these other structures, which had somewhat of the nature of personal indulgences of their emperor-creators. The palace at Antioch was the most important building in the most important city from which was ruled the eastern portion of empire.
The imperial palace is best described by Libanius in his Oration XI on the glories of Antioch:
"The palace itself has absorbed so much of the island that it covers a quarter of its area, for it is close to the centre, which it has taken as its centre too and extends to the further branch of the river. Thus the wall has pillars instead of battlements, and has been made a fitting sight for the emperor, with the river flowing at his feet and the subrubs on every side providing a feast for his eyes. Anyone who wishes to give an accurate description of this quarter must make this his whole theme, not a portion of any other. Yet this much I must explain, that of all the palaces in the world, which are called palaces from their size or are far famed for their beauty, this palace quarter in in no way inferior to the first and is far superior to the second. Its claims to beauty are unsurpassed, and it wins on all counts in any comparison of its size, for it is divided up into so many rooms, colonnades and halls that even people long acquainted with the place can lose their way when going from one door to another."
If the historical accounts can be believed the palace and much of the Island were flattened in the earthquake of 526 AD. This was swiftly followed by another massive quake two years later and then the Persian invasion. The response was the rebuilding of the walls by Justinian and Theodosios and the Island was left outside the city walls. The area thus became a sort of no-man's land and seems to have been stripped of all materials that were movable. The Imperial Palace was no more.
Evagrius makes the following comments on the palace:
"The palace of the city of Antioch is washed on the north by the river Orontes : on the south there is a large portico with two stories which touch the walls of the city, and which have two high towers. Between the palace and the river is a public road leading from the city to the suburbs".