Horses Arse.

The US “standard” railroad gauge (that’s the distance between the rails) is 4 feet, 8.5 inches. That's an exceedingly odd number for a “standard”. This gauge was used because English expatriates built the US Railroads and that's the way they built them in England. The first rail lines in England were built by the same people who built the pre-railroad tramways, and that's the gauge they used. That’s because the people who built the tramways used the same jigs and tools that they used for building wagons, which used that same wheel spacing. The wagons had this odd wheel spacing because 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 in those old long-distance roads. Imperial Rome built the first long distance roads in Europe (and England) for their legions. The roads have been used ever since. 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 therefore derived from the original specifications for an Imperial Roman war chariot.
And bureaucracies live forever.
So the next time you are handed a specification and told “we have always done it that way” and wonder what horse's ass came up with that, you might be exactly right, because the Imperial Roman war chariots were made just wide enough to accommodate the back ends of two war horses.
But the story doesn’t end there... Picture 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 railway 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 railway track, and the railway 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 backside