When Vitiges, king of the Goths, besieged Belisarius in Rome in 536, and
caused the fourteen large aqueducts to be stopped, the city was
subjected to great distress, not on account of the want of water in
general, for it was secured against that inconvenience by the Tiber, but
on account of the loss of that water which the baths required, and,
above all, of that necessary to drive the mills, which were all situated
on these canals. Horses and cattle, which might have been employed in
grinding, were not to be found; but Belisarius, a man of great
ingenuity, devised an expedient to remedy this distress. Below the
bridge that reached to the wall of Janiculum, he extended ropes, well
fastened, and stretched across the river from both banks. To these he
affixed two boats of equal size, at the distance of two feet from each
other, where the current flowed with the greatest rapidity, under the
arch of the bridge; and, placing large millstones on one of the boats,
suspended in the middle space a machine by which they were turned. He
constructed at certain intervals on the river other machines of the same
description, which, being put in motion by the force of the water that
ran below them, drove as many mills as were necessary to grind
provisions for the city. To destroy these, the besiegers threw into the
stream logs of wood, and dead bodies, which floated down the river into
the city; but the besieged, by making use of booms to stop them, were
enabled to drag them out before they did any mischief. This is said to
have been the first invention of floating mills.
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