1754 is a good start.
I googled some more.
Googling for latin-language latin grammars takes us back further in time:
But that’s still way to late.
People have been studying Latin for far longer than that. And before that, ancient Greek.
I googled some more.
And found a certain Διονύσιος ὁ Θρᾷξ, also known as Dionysios Thrax, who probably lived in the second century BC.
He wrote a grammar of the Greek language.
An English translation can be found here, and on page 10 that reads:
There are five Cases, the right, the generic, the dative, the
accusative, and the vocative. The right case is called also
the nominative and the direct; the generic, the possessive, […]
Roman grammarians just tacked the ablative on at the end.
So, it’s official: This is how it has been for over two thousand years. This is the only true case order for indo-european languages that have grammatical cases.
