from
The Collaborative International Dictionary of English v.0.48
Martello tower \Mar*tel"lo tow`er\ [It. martello hammer. The
name was orig. given to towers erected on the coasts of
Sicily and Sardinia for protection against the pirates in the
time of Charles the Fifth, which prob. orig. contained an
alarm bell to be struck with a hammer. See {Martel}.] (Fort.)
A building of masonry, generally circular, usually erected on
the seacoast, with a gun on the summit mounted on a
traversing platform, so as to be fired in any direction.
[1913 Webster]
Note: The English borrowed the name of the tower from Corsica
in 1794.
[1913 Webster]