It is likely that these items were preserved originally in Alexandria, where the people he was addressing lived. This was the largest city of the Mediterranean in his time, and probably the wealthiest city in the world. It had been founded by Greeks (well, Macedonians) and built from scratch when they took over Egypt from the Persians, around 330 B.C.

Alexandria was a center of mathematical research funded by the rulers of Egypt, and it is because of this Hellenistic culture that we have any Greek mathematical works at all. Archimedes wrote in a dialect of Greek different from that spoken by the Greeks of Alexandria or Athens. An historian I know speculates that even though traces of this dialect remain in what we have, the scribes who copied his work probably made small adjustments to his spelling, perhaps not even consciously. It is very important in dealing with mathematics that originated before printing that every manuscript was subject to errors in copying. This is not a minor consideration.