The Sea of Fertility (豊饒の海, Hōjō no Umi) is a tetralogy of novels written by the Japanese author Yukio Mishima. The four novels are Spring Snow (1969),[1] Runaway Horses (1969), The Temple of Dawn (1970), and The Decay of the Angel (1971).[2] The series, which Mishima began writing in 1964 and which was his final work, is usually thought of as his masterpiece. Its title refers to the Mare Fecunditatis, a lunar mare. The first English translated editions by Alfred A. Knopf and the Charles E. Tuttle Company featured cover designs by the graphic artist Joseph del Gaudio.