Although archaeological evidence of seaweed is hard to find because of its easy decomposition, some plant remains of wakame seaweed are found in some ruins of the Jōmon Period which leads to the supposition that kombu was also eaten at that time. As to surviving documents, the letters 軍布 (In Sino-Japanese reading 軍 is gun/kun; 布 is fu/pu/bu) appeared in Man'yōshū and wood strips from Fujiwara-kyō, and may have indicated kombu. The Shoku Nihongi (797) reports: in 797 of Emishi (Ainu or Tohoku region people) stated they had been offering up kombu, which grew there, as tribute to the Yamato court every year without fail. The Engishiki (927) also reports that kombu had been offered up by Mutsu.