[3] Since Gibraltar (like the United Kingdom) is outside the European Union's Schengen Area, identity checks are required to cross the border.

[4] On 31 December 2020, an agreement in principle had been agreed between Spain and the United Kingdom, for Gibraltar to join the EU's Schengen Area while remaining a British Overseas Territory.

The Lines of Contravallation were blown up by the Gibraltar Commanding Royal Engineer Charles Holloway, with permission from Spain on 14 February 1810, to avoid them falling into the hands of the approaching French.

In 1909 the United Kingdom decided to reduce the number of sentries and built a fence 7 feet (2.1 m) high,[7] however there was suspicion about the motives for doing so.

[citation needed] Spain claims that, by building the fence where it did, the United Kingdom annexed 106 of the original 156 hectares of neutral ground.

According to Article X of the Treaty of Utrecht, dominion is ceded over the town and castle of Gibraltar, together with the port, fortifications, and forts thereunto belonging.