Guarded from the outside world by a massive wall, the enclosed area inside covers 178 acres in the centre of Beijing making it the biggest palace complex anywhere in the world. Built to house the emperors of China between 1420 and 1912, it took over a million workers to construct the Forbidden City and houses some of the most precious ancient artefacts in the world. The Forbidden City has an extensive recent history of invasion with Anglo-French forces invading the palace in the Second Opium War, and the Japanese invading in 1933.