GP is probably referring to the standard railroad gauge which is alleged [1] to have been derived from the width of roman chariot wheels and which would have dr

GP is probably referring to the standard railroad gauge which is alleged [1] to have been derived from the width of roman chariot wheels and which would have driven the train tunnel width in modern times. [1] https://en.wikipedia.org/wiki/Standard-gauge_railway#Origins https://en.wikipedia.org/wiki/Standard-gauge_railway#Origins