The point at which these avenues converged was thought to be the Tetrapylon of the Elephants, which we have discussed elsewhere. However, in the 1930s, the excavators where intent upon discovering another Apollonian convergence. This was the famed Omphalos (or navel) of the city which according to Evagrius was at the point at which the Colonnaded Street met the main avenue to the Island (thus somewhere near the Forum of Valens).
Stinespring's translation of the Vatican text in Arabic states: "There is in the city a place called el-Umsilbah (ο ομπηαλοσ), the explanation of which is "the middle of the city"; and an idol is there; whenever a thief or rogue bestirs himself in the city, that idol cries out with a loud cry which is heard in the farthest limits of the city." The latter part repeats the superstitious ramblings for which the Arab author is notorious.
I was recently perusing some Seleucid coinage and came upon the image (below) of Apollo seated upon the Omphalos as supposedly was the statue situated at the Omphalos. There is a bow to Apollo's side and he is holding an arrow pointed downwards.