Because practitioners of Heian Buddhism frequently performed severe ascetic practices, incantations and prayers in the mountains, this Buddhism came to be called mikkyō. Kūkai, a Buddhist monk, learned Chinese esoteric Buddhism while on a diplomatic mission to the Chinese court, and combined Japanese Buddhism with Chinese esoteric Buddhist practices to form Japanese Shingon Buddhism. Saichō, a Buddhist monk who also journeyed to China, learned the practices of the Chinese Tendai sect and argued that the teachings of the Lotus Sutra should be the core of Japanese Buddhism.