Martello towers as compact coastal forts

What is a Martello tower, and how does it compare with castles or later coastal defenses?

Martello towers were thick-walled round forts inspired by Corsican defenses and adapted to local coastal-defense needs around the empire.

British interest in Martello towers grew from experience with a round fortress at Mortella in Corsica. The towers were heavily built, self-contained defensive cylinders with gun positions, stores, quarters, and water arrangements. Their layout can be compared with castle towers and star forts. Local engineers adapted the same basic concept for different coastal-defense problems.