Just in case you may have missed this "petit bon mot". 

Some Railroad history.
This is true, believe it or not.

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 English expatriates built the US Railroads.
Why did the English 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 have that particular odd wheel spacing? Well, if
they tried to use any other spacing, the wagon wheels would break on
some of the old, long distance roads in England, because that's the
spacing of the wheel ruts. So who built those old rutted roads?

Imperial Rome built the first long distance roads in Europe (and
England) for their legions. The roads have been used ever since.
And the ruts in the roads?

Roman war chariots formed the initial ruts, which everyone else had to
match for fear of destroying their wagon wheels.
Since the chariots were made for Imperial Rome, they were all alike
in the matter of wheel spacing.

The United States standard railroad gauge of 4 feet, 8.5 inches is derived f
rom the original specifications for an Imperial Roman war chariot.

And bureaucracies live forever. So the next time you are handed a spec
and told "We have always done it that way" and wonder what horse's ass 
came up with that, you may be exactly right, 
because the Imperial Roman war chariots were made just wide
enough to accommodate the back ends of two war horses.

Now the twist to the story...
When you see a Space Shuttle sitting on its launch pad, there are two
big booster rockets attached to the sides of the main fuel tank. These
are solid rocket boosters, or SRBs. The SRBs are made by Thiokol at
their factory in Utah. The engineers who designed the SRBs would have
preferred to make them a bit fatter, but the SRBs had to be shipped
by train from the factory  to the launch site. 

The railroad line from the factory happens to run through a tunnel in the 
mountains. The SRBs had to fit through that tunnel. The tunnel is slightly 
wider than the railroad track, and the railroad track, as you now know, is 
about as wide as two horses' behinds. So, a major Space Shuttle design 
feature of what is arguably the world's most advanced transportation system 
was determined over two thousand years ago by the width of a horse's ass.