That the first true Greek language came about because someone wanted to write down the orally transmitted works of Homer, but couldn’t because none of the existing languages in that part of the Mediterranean had any vowels – and you can’t accurately transcribe poetry [or song, either, my wife the voice professor informs me] without vowels. So this original transcriber (according to Archaeology magazine) took the vowelless Phoenician alphabet and added Greek vowels, and within a hundred years ancient Greeks became literate on a wide scale.
Now, for purists, there were two prior Greek languages, known as Linear A, which has yet to be deciphered/translated, and Linear B, but it is likely Linear A was without vowels, and Linear B was definitely without vowels and was exclusively used by a very limited number of bureaucrats and merchants for record-keeping, primarily of commodities and taxes. Definitely not for poetry or literature, or even science fiction or fantasy. Roughly a hundred to two hundred years before the Greek introduction of vowels, the same transition took place in ancient Israel [so, yes, the Jews were first to add vowels to the Phoenician alphabet, but word, literally, traveled slowly in those days].
Apparently, the Greek version of language with vowels was more effective than the Hebrew version, possibly because even then entertainment topped scripture, but that also might have been because Alexander the Great conquered more territory and imposed Greek on more people. The Romans, the great practical engineers, adopted/stole everything Greek, including the idea of vowels, but streamlined and simplified the alphabet in the Latinate letters that the majority of the world uses today.
And that’s why, when I include poetry and flowery language in my books, to the dismay of the action-preferred readers, everyone can read it… all because [take your pick], ancient Hebrews wanted more descriptive language in their scriptures or ancient Greeks wanted to be able to preserve the works of Homer.