Palaia means "ancient" and was used to refer to one of the major churches in Antioch to discriminate it from the Great Church (the Golden Octagon) that I have written on elsewhere. Boucher states in his Short History that "the earliest ecclesiastical building, called Palaia, or Apostolic, traditionally ascribed to Theophilus the friend of St. Luke, was believed to stand on the spot where the Apostles first delivered their addresses. This seems to have disappeared in the persecution of Diocletian, and it is doubtful whether the church begun by Constantine and also called Apostolic was on the same site".
If Boucher was right (and he was wrong on some other details in his book) then the site of the first preaching was the Singon (or Siagon) Street that I have discussed elsewhere. This, by implication might also signal that the Palaia was at this site which some feel might be closer to the Beroea Gate than the old centre of the Seleucid city.
The Palaia, according to Wendy Mayer, was the main preaching pulpit for John Chrysostom. She speaks of it dating back to the time of the Apostles and cites Eltester 1937 (pgs 272-3). She sites it in the Old Town because it was the Old Church... The Siagon ("jawbone") street was so called because it was not straight and that does not appear to signify a street in the strictly Hippodamian Old Town. Just because the church was called "ancient" does not mean it must be in the most "ancient" part of the town.
Pietro Rentinck in his book "La cura pastorale in Antiochia nel IV secolo" says that the church was rebuilt and expanded under the bishop Vitale (around 314 AD) and after his death the work was completed by Filogonio (319-324 AD). He feels the church may have been reconstructed in a basilica form at that time. He says the sources are silent on the dimensions of the structure.