Master Dogen (1200-1253 C.E.) brought the Soto branch of Zen Buddhism to Japan after his 1223 visit to China. Master Keizan (1268-1325 C.E) initiated the great social development of the Soto sect throughout Japan. Thanks in large part to these individuals, Soto Zen Buddhism has gained great popularity in Japan and throughout the world. For the lay believers of Soto-shu, it can be said that Dogen Zenji and Keizan Zenji are, in terms of their faith, like father and mother. By the Eastern calendar, Dogen Zenji died on August 28, 1253 at the age of 53 and Keizan Zenji died on August 15, 1325 at the age of 58. According to the Western calendar, both of these dates fall on September 29th. On this day, a ceremony called Ryosoki is respectfully held at Soto-shu temples to honor these two important ancestors.