E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Aristophns calls Athens oεo (Equits, 1323 and 1329), and again in the Acharnians, 637. Macaulay uses the phrase, city of the violet crown. Ion (a violet) was a representative king of Athens, whose four sons gave names to the four Athenian classes; and Greece in Asia Minor was called Ion-ia. Athens was the city of Ion, crowned king, and hence the Ion crowned or violet-crowned.
Similarly Paris is called the City of Lilies, by a pun on the word Louis (lys, a lily).