A horses' ass

It starts with Railroad Tracks.
The US standard railroad gauge (distance between the rails) is 4 feet 8.5 inches, which is an exceedingly odd number.

Why was that gauge used? Because that's the way they built them in Scotland, and Scottish expatriates designed the US railroads.

Why did the Scottish build them like that? Brcause 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 had used for building wagons....which used that wheel spacing.

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

So who built those old rutted roads?
Imperial Rome built the fdirst long distance roads in Europe (including Scotland) for their legions. These roads have been used ever since.

And the ruts in the roads?
Roman war chariots formed the initial ruts, which everone 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.
Therefore the United States Railroad gauge of 4ft 8.5 inches is derived from the original specification of the Roman war chariot. Bureaucracies live forever.......

Imperial Roman army chariots were made just wide enough to accomodate the rear ends of two war horses. (Two horses asses).

Now there is a twist to this 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 SRB's.
The SRB's are made by Thiocol at their factory in Utah.

The engineers who designed these boosters would have liked to make them a bit fatter, but they had to be shipped by train from the factory to the launch site.
The Railroad line from the factory happens to run into a tunnel in the mountains, and the SRB's had to fit through that tunnel.
The tunnel is slightly wider than the Railroad track, and the railroad track as you know is about as wide as two horses' behinds.

So a major Space Shuttle design feature, of what isarguably the world's most advanced transportation system, was actually determined over 2000 years ago by the width of two horses asses!

And you thought that being a horses's ass wasn't important?

Ancient horses' asses control almost everything.