On a hill above the East Pier is a Martello Tower (one of two that can be found on Howth Head). It dates from 1805 and was built by the Englishman, who built several Martello Towers around the Irish coast to watch out for an invasion by Napoleon and the French.
The towers are round with a flat roof.
It’s difficult not to notice the chubby shape of the local Martello Tower from any part of Howth. These defensive bastions were constructed by the Britons during the 19th century all around the Irish coast (34 of them, my travel book insists in pointing me), and they main purpose were to defend the island against the menace of Napoleonic troops.