There are 28 towers in Ireland. The original name of Martello Tower was Mortella. They changed it to Martello after a bit of time. They were first made to defend from the French in 1900. They were also used in the Easter rising most of them are now houses, hotels, museums or a pile of rubble.
They were used in the easter rising, but they were actually built to defend from the French and Napoleon. The Martello towers are made out of a thick layer of stone about 3 meters thick. One of the walls of the Martello tower on Sandymount contains a spiral starecase. As the entrances were placed on the first floor to help defend against attackers.
The Sandymount Martello tower was seen many uses since is was used during battles and wars. At one point is was a waiting area for the local tram stop, that was when the door was cut into the wall. It has also been the sight of shops and restaurants over the past 100 years. Most recently a restaurant was built but was unable to open due to health and safety concerns.