In many places there are streams of water which swell for six hours
and ebb for six hours; and I, for my part, have seen one above the
lake of Como called Fonte Pliniana, which increases and ebbs, as I
have said, in such a way as to turn the stones of two mills; and
when it fails it falls so low that it is like looking at water in a
deep pit.

[Footnote: The fountain is known by this name to this day: it is
near Torno, on the Eastern shore of Como. The waters still rise and
fall with the flow and ebb of the tide as Pliny described it (Epist.
IV, 30; Hist. Nat. II, 206).]