Esther 1:1 says:
Now it came to pass in the days of Ahasuerus -- he was the Ahasuerus who reigned from Hodu to Cush, one hundred twenty-seven provinces.
For historical context, the period of the Persian Empire that forms the historical backdrop for the story of Purim and Megilat Esther, known as the Achaemenid Empire, took place from 550 to 330 BCE (Darius 1, who ruled from 522 to 486 BCE, allowed the reconstruction of the Second Temple in Jerusalem.) (link). According to the 5th century BCE Greek historian Herodotus, the Achaemenid Empire was divided into 20 districts or provinces called satrapies ruled by Medo-Persian satraps based on the various kings and governors of the conquered lands, and that different provinces would have different taxes imposed on them (link, list of provinces as per Herodotus, map).
Now, 20 provinces and 127 provinces are very different. Could "127" be referring to cities (with a few cities per province, not sure how it might be counted that way)? Or perhaps 127 refers to the more distinct cultures within the provinces (e.g. at the time, Phoenicians, Jews, and people living in Cyprus were ruled as a single province, although I don't know if even this approach would quite reach 127)? Might it been like one of the 20 provinces could have been considered to have a number of smaller counties (just a guess, don't know of any historical support)? Is it possible that the text could have meant something like "7 regions, 20 provinces, and 100 sub-provinces" (the Hebrew is phrased "seven and twenty and one hundred provinces" which seems to traditionally just be taken as an archaic way of writing 127)?
So my question is, what type of "province" exactly does "one hundred twenty-seven provinces" refer to?