Walls have been built since ancient times, to mark borders, protect kingdoms and settlements, or keep out unwanted people. In more recent times, walls have also been built to serve as memorials and structures of art.

01. Chewing Gum Wall, Seattle, US



Not all walls are controversial and divisive. Seattle's gum wall is the place for any unwanted chewing gum, a tradition which was started by people queuing for the theatre. Currently the gum on the wall stretches to several inches thick and is a slightly alternative location for wedding photographs.

03. Security Wall, West Bank, Israel



This wall is the most controversial in the world. It is being constructed by the Israeli government to separate the Israeli and Palestinian people of the West Bank. Currently standing at 8m (26ft) high, this wall remains a source of hostility and resentment between the two peoples.

05. Belfast Peace Line, Belfast, Northern Ireland



The Peace Line stands over 20ft (6m) high and was constructed to separate Catholic and Protestant communities in Belfast thereby 'keeping the peace'. What was meant as a temporary measure became more permanent as the barriers became longer and wider. The recent suggestion that they should be destroyed was met with anger from local residents and so its deconstruction remains a debated topic.