The turtle-back tombs are thought to have been introduced into the Ryūkyū Kingdom from Fujian in the late 17th or early 18th century ("in the interval between the careers of Shō Shōken and Sai On", according to Gregory Smits' monograph on the intellectual history of the Ryūkyū Kingdom [REF].
In the spring of 1945, during the Battle of Okinawa, many Okinawan civilians sought refuge from the naval bombardment of the island inside their ancestors' turtle-back tombs,[REF][REF] just like the characters of Oshiro's short novel [REF].