There are no mountains in Bangkok. The closest mountain range is the Khao Khiao Massif, about  southeast of the city. Phu Khao Thong, the only hill in the metropolitan area, originated with a very large chedi that King Rama III (1787–1851) built at Wat Saket. The chedi collapsed during construction because the soft soil could not support its weight. Over the next few decades, the abandoned mud-and-brick structure acquired the shape of a natural hill and became overgrown with weeds. The locals called it ''phu khao'' (), as if it were a natural feature. In the 1940s, enclosing concrete walls were added to stop the hill from eroding.