Lagrange's Four Square Theorem/Historical Note

Historical Note on Lagrange's Four Square Theorem
It is suggested by some sources that the result of Lagrange's Four Square Theorem was known, at least empirically, by.

Some sources suggest that the theorem was originally stated formally by.

However, it appears that published the results of his having tested it thoroughly up to $120$, and stated the theorem in his $1621$ translation of the  of.

read about it in his copy of that work, and studied it, but appears to have failed to find a proof, as no proof of his can be found.

Some sources claim that its first proof was by, but this is questionable.

It was finally proved by in $1770$.