Gibraltar is a British Overseas Territory and city located at the southern tip of the Iberian Peninsula, bordered to the north by Spain (Campo de Gibraltar). It is a heavily fortified British air and naval base that guards the Strait of Gibraltar, which is the only entrance to the Mediterranean Sea from the Atlantic Ocean. Gibraltar was captured by the British Fleet in 1704 during the war of the Spanish Succession and was ceded to Britain under the Treaty of Utrecht in 1713. Gibraltarians overwhelmingly rejected proposals for Spanish sovereignty in a 1967 referendum, and for shared sovereignty in a 2002 referendum. Gibraltar is not a sovereign state, and its formal international relations are the responsibility of the Government of the United Kingdom.