Which was the most southern border city of Byzantine Empire, before Arab conquest?

Since Andrew has blocked me, I have to add a correction here to Dimitris Sotiropoulos on https://www.quora.com/Which-was-…

Iotabe is identified tentatively with Tiran Island, 27°57′N 34°33′E

Syene is Aswan, 24°05′20″N 32°53′59″E

Berenice Troglodytica is 23°54′38″N 35°28′34″E

So Iotabe is not the southernmost point, unless Dimitris has evidence for an alternate identification of Iotabe as being south of Aswan.