> For some reason—whether a sense that there was some mistake, or someone copied something down wrong, or because it was so absurd—the manuscripts we have show that Heron ignored the minus sign and gave the answer as √63 instead.

I wonder if the minus sign was in use in the time of Heron (First century AD). I couldn't tell from this Wikipedia page https://en.wikipedia.org/wiki/Plus_and_minus_signs