  Here we show how spacetime transformations consistent with the principle of
relativity can be derived without an explicit assumption of the constancy of
the speed of light, without gedanken experiments involving light rays, and
without an assumption of differentiability, or even continuity, for the
spacetime mapping. Hence, these historic results could have been derived
centuries ago, even before the advent of calculus. This raises an interesting
question: Could Galileo have derived Einsteinian relativity?
