The Pool of Blood was literally a giant subterranean chamber built and used by the Church of Blood.
Brother Blood filled the pool with the blood of human sacrifices and regularly bathed in it in order to replenish his strength and vitality. Blood's son, the first Brother Blood born in the 20th century, succeeded to the rank of cult leader by fighting and ultimately slaying his father inside the Pool of Blood. The original Pool of Blood was located at the Church's headquarters in Zandia, but a second one was constructed in a cave beneath another church in Phoenix, Arizona.
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