By 1534, all the major islets of the island group were identified and named in the book Record of the Imperial Envoy's Visit to Ryukyu (使琉球錄). And were the Ming Dynasty's (16th-century) sea-defense frontier. One of the islands, Chihweiyu, Marked the boundary of the Ryukyu Islands. This is viewed by the PRC and ROC as meaning that these islands did not belong to the Ryukyu Islands.