Martello Tower, The Cliff Path, Howth, County Dublin, Leinster, Republic of Ireland, Europe

Martello Tower No 5, L'Ancresse Bay, Guernsey, Channel Islands, United Kingdom, Europe

Martello Tower, Tower T, Felixstowe, Suffolk, England, United Kingdom, Europe

Martello Tower, with walls up to 11 feet thick and surrounded by dry moat, at Ferry Reach, built by the British Army in 1883 to protect the main channel into Bermuda, St. George's Island, Bermuda, Atlantic, North America

Martello Tower, with walls up to 11 feet thick and surrounded by dry moat, at Ferry Reach, built by the British Army in 1883 to protect the main channel into Bermuda, St. George's Island, Bermuda, Atlantic, North America

Antony Gormley's sculpture of a man looking out to sea, standing on the Napoleonic Martello tower in Aldeburgh, Suffolk, England, United Kingdom, Europe

Antony Gormley's sculpture of a man looking out to sea, standing on the Napoleonic Martello tower in Aldeburgh, Suffolk, England, United Kingdom, Europe

Martello towers, watch and guard towers from the 17th century found along the coastline, here Tower No. 5 at Pembroke Bay in the northeast of Guernsey, Channel Islands, Europe

Royal Guernsey Golf Club, Martello towers, watch towers and fortified towers built in the 17th century, next to the fairways, at Pembroke bay in the northeast of the Channel Island of Guernsey, Europe

Martello towers, watch and guard towers from the 17th century found along the coastline, here Tower No. 5 at Pembroke Bay in the northeast of Guernsey, Channel Islands, Europe