Round, grooved and underfoot

Why is this strange object in the Alexandria sidewalk?

A few blocks from our Alexandria headquarters there is an unusual round stone set among the normal concrete slabs of the sidewalk (see photo).  There are many things it might be (or might have been before it became pavement).  A stone wagon wheel?  There were such things, but even historic Alexandria doesn’t go back that far, and it would have been too heavy to use on the muddy Colonial tracks.  The fossil of some strange radial-boned ancient jellyfish?  The grooves are rather too straight and regular for that, we think; it’s almost certainly artificial.  (However, we defer to any paleontologist who may have more informed ideas in that area.)  Perhaps it’s some art installation, a sculpture set underfoot making a statement about something, though it’s rather far from the Torpedo Factory and other Alexandrian artistic establishments.

But it’s actually a lower millstone.  The grain to be ground was fed in through a hole in the center of the top millstone.  As the stone turned the grain would be forced radially outward by the grooving, in the process being turned from individual berries of wheat or corn into a fine powder.  But imagine how carefully it would have to be done!  The spacing between the stones could not be too small, or nothing would move; nor too large, for no grinding would happen then.  The rate of feeding grain must be adjusted; the speed of the rotating stone controlled; no doubt there were other considerations that don’t even occur to us.  And all this happened when the source of power was the capricious wind, or the water level in a stream, or maybe harnessed donkeys.  The result was not just acceptable food most of the time, but flour of any grade of fineness, sieved to the desired color.

Also, in support of this process there was an industry of specialists: those who could put together the big machine that is a mill, as well as run it.  And maintain it.  There existed (and probably still exists) that tiny elite of artisans, the millstone-cutters, those who could re-cut the grooves properly when they got worn down by the work.  We suspect that there are subtleties to that process beyond what we imagine.

This is very old technology.  Windmills are a relatively new part of it, being an invention of about the twelfth century; the rest is older.  It may appear crude compared to, say, an electric scooter or a ball-point pen.  But, as we’ve pointed out with church bells, old technology is not necessarily simple.