The growth of Gibraltar onto the southern half of the isthmus began with the construction of two forts in the northernmost part of the ceded territory. In 1815, Gibraltar suffered a yellow fever epidemic. This led to a Spanish concession so a temporary quarantine health camp could be built on the isthmus. After the plague was over, the British did not remove the camp. In 1854, a new epidemic prompted more health camps, which eventually gained Gibraltar these extra 800 metres of land. The occupation of the isthmus culminated in 1938-1939 with the construction of the aerodrome during the Spanish civil war.