Spain, Castile, Segovia, Puerta de San Andrés or St Andrew's Gate, part of the city's medieval defensive fortifications.

Fortification built on the end of Hurst Spit at the narrowest point of the Solent, opposite the Isle of Wight guarding the approaches to Southampton Port and Portsmouth harbour. First fort completed i...

Qatar, General, Aerial view of Zubara fort with the desert beyond.

Northern Ireland, County Derry, The Guild Hall, view from the city's 17th century walls with a cannon in the foreground.

Northern Ireland, County Derry, The Guild Hall, view from the city's 17th century walls with a cannon in the foreground.

Northern Ireland, County Derry, The Guild Hall, view from the city's 17th century walls with a row of cannons in the foreground.

Northern Ireland, County Derry, The Guild Hall, view from the city's 17th century walls with a cannon in the foreground.

Italy, Valle d'Aosta, castle towers, Fenis Castle.

Italy, Valle d'Aosta, Fenis Castle.

Ethiopia, Gonder, Royal Enclosure.

Germany, Mecklenburg-Vorpommern, Rostock, Stone Gate.

Italy, Campania, Naples, Castel Nuovo, also known as Maschio Angioino.