Persia
The Persian Empire, ruled by the Achaemenid kings in Thucydides' day and by the Sasanian kings in Procopius'.
Today: Iran
The Plague at Athens, and Pericles Answers the Athenians
Thucydides, History of the Peloponnesian War, Book 2 (sections 47–65) · after 430 BCE (events of 430–429 BCE)
ἤρξατο δὲ τὸ μὲν πρῶτον, ὡς λέγεται, ἐξ Αἰθιοπίας τῆς ὑπὲρ Αἰγύπτου, ἔπειτα δὲ καὶ ἐς Αἴγυπτον καὶ Λιβύην κατέβη καὶ ἐς τὴν βασιλέως γῆν τὴν πολλήν.
It began, people say, in Ethiopia, beyond Egypt. From there it spread down into Egypt and Libya and across most of the Persian Empire.
The Plague at Constantinople
Procopius, History of the Wars, Book 2 (chapters 22–23) · c. 550 (events of 542; Books 1–7 made public in 551 at the earliest)
τὰ μὲν οὖν ἀμφὶ τῷ λοιμῷ ἔν τε τῇ ἄλλῃ Ῥωμαίων γῇ καὶ ἐν Βυζαντίῳ ταύτῃ πη ἔσχεν. ἐπέσκηψε δὲ καὶ ἐς τὴν Περσῶν γῆν καὶ ἐς βαρβάρους τοὺς ἄλλους ἅπαντας.
That, roughly, is how things went with the plague in the rest of the Roman land and in Byzantium. But it also struck the Persians' land, and all the other barbarians.