Did they confuse hectares with square kilometers?
56 sq KM is 21 sq miles of mausoleum; 56 hectares is 138 acres.
Mausoleum of QinshihuangIn 246 BC, after Qin Shihuang (means "the first emperor of the state of Qin" in Chinese) ascended the throne of Qin ( a state in that period), he ordered to build his final resting palace. This authoritative emperor left behind the world with great achievement and mysterious royal mausoleum as well. The construction lasted 38 years, confiscating over 720000 corvees and prisoners. Modern surveys of the site show that the mausoleum is indeed divided into an inner sanctuary and outer city. According to historical record, the mausoleum originally has 250000 sq. meters built-up area at the bottom and 115m high. Unfortunately, because of erosion and man-made breach, the mausoleum currently remains 120000 sq. meters at the bottom and 87 meters high. Around the mausoleum, there are lots of accompanying tombs, which consist of 56.25 sq. km tomb area. In addition to the discovered Terracotta Warriors and Bronze Horses, there are more vaults containing other relics being discovered recently. As time goes by, it's bound to discover more relics. Mausoleum of Qin Shihuang boasts a Chinese history museum, therefore, it's well-known to the outside world.