9世纪初叶,新罗人张保皋入唐担当武宁军小将,后来返回新罗,被新罗王委任为清海镇海洋大使。张保皋利用9世纪后东亚三国民间旺盛的贸易,将山东半岛登州,以及新罗莞岛作为根据地(特别是登州赤山浦海湾一带),开始了横跨黄海,遍及唐朝、新罗、日本三国波澜壮阔的海洋活动。他的事迹引起唐朝著名诗人杜牧的兴趣,撰有《张保皋、郑年传》,以至于成为欧阳修撰修《新唐书》的素材,并被高丽时代金富轼 In the early 9th century, the Silla people Zhang Baogao entered the Tang as a Wuning Jun and later returned to Silla, who was appointed as the sea ambassador of Qinghai by the Silla King. Zhang Baogao started his trade across the Yellow Sea across the Yellow Sea, the Tang Dynasty, Silla, Japan, using Dengzhou, a Shandong peninsula, and Xinluo Wandao as bases (especially in the area along Chundu Bay in Chishan) Three magnificent ocean activities. His deeds aroused the interest of Du Mu, a famous poet of the Tang Dynasty. He wrote “Zhang Baogao and Zheng Nian Zhuan” so that he became the material of Ouyang Xiu’s compilation of “New Tang Book,” and was used by the Kofee era Jin Fushi