Why are all ancient Persian names written in their Greek forms?

Because, for a very long time, the West only knew of Persian historical figures through Greek sources. And even if they didn’t, the prestige of Greek and Latin meant that names mediated thorough those languages were more familiar. Thus, Cyrus, Ramses, and Moses.

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.