Noun
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.
Source: Webster's dictionarySouth Walls has a 19th-century Martello tower and is connected to Hoy by the Ayre. Source: Internet
Minorcan countryside Cala Trebalúger Martello tower, Alcaufar with Illa de l'aire lighthouse in the distance. Source: Internet