Wikipedia
Hitobashira (人柱 human pillar), practiced formerly in Japan, is a human sacrifice, buried alive under or near large-scale buildings like dams, bridges, and castles, as a prayer to the gods so that the building is not destroyed by natural disasters such as floods or by enemy attacks. Hitobashira can also refer to workers who were buried alive under inhumane conditions.
Some of the earliest written records of hitobashira can be found in the Nihon Shoki (The Chronicles of Japan). One story centered on Emperor Nintoku (323 A.D.) discusses the overflowing of the Kitakawa and Mamuta Rivers. Protection against the torrent was beyond the ability of the stricken populace. The Emperor had a divine revelation in his dream to the effect that there was a person named Kowakubi in the province of Musashi and a person called Koromono-ko in the province of Kawachi. If they should be sacrificed to deities of the two rivers respectively, then the construction of embankments would be easily achieved. Kowakubi was subsequently thrown into the torrent of the Kitakawa river, with a prayer offered to the deity of river. Through the sacrifice it was possible to construct the embankment completely, Koromono-ko however escaped being sacrificed. The Yasutomi-ki, a diary from the 15th Century documents the famous tradition of "Nagara-no Hitobashira". According to the tradition, a woman who was carrying a boy on her back was caught while she was passing along the river Nagara, she was buried at the place where a large bridge was then to be built. Hitobashira traditions are almost always connected with complex and dangerous projects that were required to be built and mostly with water. The stories of hitobashira were believed to inspire a spirit of self-sacrifice in people.
Stories of hitobashira and other human sacrifices were common in Japan as late as the sixteenth century. Hitobashira is no longer practiced in construction.