The Origin of the Military Specification The US Standard railroad gauge (distance between rails) is 4 feet,

The Origin of the Military Specification
The US Standard railroad gauge (distance between 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 first U.S. railroads were
built by English expatriates.
Why did the English people build them like that? Because the first rail
lines in Europe were designed and 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 designed and
built the tramways used the same jigs and tools that they used for building
wagons, which used that same wheel spacing.
Okay, why did the wagons use that odd wheel spacing? Well, when they tried
to use any other spacing, the wagons were prone to breaking down 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 for centuries. 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 all made to certain specifications 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 (Military, as it were) for an Imperial Roman army war chariot.
But one "nagging" question still remains. Why did the design of the Roman
army war chariots incorporate that specific wheelbase?
Answer:
Because the chariots were designed to be just wide enough to accommodate the
back ends of two war horses.
So, the next time you are handed some odd ball specification and you assume
that some horse's ass was responsible for coming up with it, you may be
exactly right!