In those days, Silla was sending the envoys to Changan to give tribute to the emperor of Tang most frequently among other countries, and under normal conditions, the route via Silla was the fastest way to Japan; however, it was out of the question because there was a possibility of war between Japan and Silla in consideration of the purpose of sending the envoys to Tang China.
当時は新羅が最も頻繁に長安に朝貢しており、普通なら新羅経由で帰国するのが近道だが、遣唐使発遣の事情を考えてみれば、日本と新羅は開戦する可能性もあり、新羅経由は取れなかった。