s possible for a man on horseback to ride in them.[101]
And Belisarius arranged for the defence of the city in the following
manner. He himself held the small Pincian Gate and the gate next to this
on the right, which is named the Salarian. For at these gates the
circuit-wall was assailable, and at the same time it was possible for
the Romans to go out from them against the enemy. The Praenestine Gate
he gave to Bessas. And at the Flaminian, which is on the other side of
the Pincian, he put Constantinus in command, having previously closed
the gates and blocked them up most securely by building a wall of great
stones on the inside, so that it might be impossible for anyone to open
them. For since one of the camps was very near, he feared least some
secret plot against the city should be made there by the enemy. And the
remaining gates he ordered the commanders of the infantry forces to keep
under guard. And he closed each of the aqueducts as securely as possible
by filling their channels with masonry for a considerable distance, to
prevent anyone from entering through them from the outside to do
mischief.

But after the aqueducts had been broken open, as I have stated, the
water no longer worked the mills, and the Romans were quite unable to
operate them with any kind of animals owing to the scarcity of all food
in time of siege; indeed they were scarcely able to provide for the
horses which were indispensable to them. And so Belisarius hit upon the
following device. Just below the bridge[102] which I lately mentioned as
being connected with the circuit-wall, he fastened ropes from the two
banks of the river and stretched them as tight as he could, and then
attached to them two boats side by side and two feet apart, where the
flow of the water comes down from the arch of the bridge with the
greatest force, and placing two mills on either boat, he hung between
them the mechanism by which mills are customarily turned. And below
these he fastened other boats, each attached to the one next behind in
order, and he set the water-wheels between them in the same manner for a
great distance. So by the force of the flowing water all the wheels, one
after the other, were made to revolve independently, and thus they
worked the mills with which they were connected and ground sufficient
flour for the city. Now when the enemy learned this from the deserters,
they destroyed the wheels in the following manner. They gathered large
trees