The quadrangle fort, formerly known as the Yongkang Fort. Because the fort is long and wide like a quadrangle, it is commonly known as the "quadrangle fort". According to Gu Yuzhang's "Humen Inland River Battery Map" (manuscript): The Sifang Battery is an important stronghold of Guangzhou City Defense, "49 feet and nine feet around the outer platform, one foot and seven feet high; 16 feet and eight feet around the Taizhongzi platform, two feet and one foot high.