Why are railroads 4'8 1/2" in the US?

> What's True: The standard U.S. railroad gauge is similar in width to the wheel spacing of Roman chariots.

> What's False: That similarity is based much more on coincidence and inherent physical limitations than a direct line of imitation.

> ... claims about a direct line descent between ancient Roman chariot tracks and the standard U.S. railway gauge jump the tracks when confronted with the fact that despite some commonality of equipment, well into the 19th century the U.S. still did not have one "standard" railroad gauge.

The nature of the country indirectly defines the required track gauge.