"Accretion" is right.
But, have to point out that the so-called "Persian Empire" has a distinct history before Cyrus, and even the Median Empire. It just isn't well-known to even the Persians Iranians) themselves. This is before the neo-Assyrian Empire..
As you point out, Cyrus (Kourosh) the Great, was the grandson of of the Median Emperor (Cyrus' mother, if am not mistaken, was a Median herself), and Cyrus, actually married a Median Princess, himself. That union helped, later, with uniting the Medians (current kurds) with the Persians. Both being of Aryan roots, but different tribes, at the time.
However, in strictly Aryan terms/history (Iran in particular), that history (or pre-history) began with the Pishdadians Dynasty. Remember "Jamshid" and Norooz or as the Parsee Zoroastrian community in India call it "Navroz" Jamshidi?
While I am on this subject, it is fascinating to find out more about it.
Even Ferdowsi's Shah-Nameh (Book of Kings), which is a very significantly piece of literary & historical work (written circa 10th century AD), explicitly goes well beyond Cyrus the Great "Persian Empire" and talks about other Aryan Dynasties of Iran, namely, the Pishdadians and Kianians.
Well worth reading if interested in history: Pre Cyrus the Great Aryan Dynasties of Iran - Epic Cycles
significantly piece = significant piece
Interesting.
However, as far as I can tell, these stories are mythical in nature rather than historical.
As I’ve said elsewhere, I don’t dismiss myth as inherently untruthful, but I prefer to see it backed up with some genuine historical evidence from archaeology, etc. King Arthur is probably based on a historical figure, but the Camelot of the stories never really existed.
Good point, however I meant specifically the Achaemenids, not the overall Aryanic realm. it's interesting that Jamshid is the iranic version of the Indic Yama -- who is the Indic god of death who rides a buffalo and who bears much of the aspects of an Asura (and I think is named as such along with Varuna and Agni in the Rigveda)