The US Standard railroad gauge (distance between the rails) is 4 feet, 8.5 inches. That's an
exceedingly odd number. Why was that gauge used? Because that's the way they built them in
England, and the US railroads were built by English expatriates.

Why did the English people build them like that? Because the first rail lines were built by the
same people who built the pre-railroad tramways, and that's the gauge they used.

Why did "they" use that gauge then? Because the people who built the tramways used the same jigs
and tools that they used for building wagons, which used that wheel spacing.

Okay! Why did the wagons use that odd wheel spacing? Well, if they tried to use any other
spacing the wagons would break on some of the old, long distance roads, because that's the
spacing of the old wheel ruts.

So who built these old rutted roads? The first long distance roads in Europe were built by
Imperial Rome for the benefit of their legions. The roads have been used ever since. And the
ruts? The initial ruts, which everyone else had to match for fear of destroying their wagons,
were first made by Roman war chariots. Since the chariots were made for or by Imperial Rome they
were all alike in the matter of wheel spacing.

Thus, we have the answer to the original questions. The United States standard railroad gauge of
4 feet, 8.5 inches derives from the original specification for an Imperial Roman army war
chariot. Specs and Bureaucracies live forever. So, the next time you are handed a specification
and wonder what horse's rear end came up with it, you may be exactly right.

Because the Imperial Roman chariots were made to be just wide enough to accommodate the
back-ends of two war horses.