In 1173 Kiyomori sent toreishi (errand to return call or visit), got the license for passage of merchant ships to Owada no tomari from Goshirakawa, made the Sung merchant ships pass through Seto Inland Sea and expanded the trade between Japan and Sung Dynasty in China because Goshirakawa gave a present to the Sung messenger in return and the diplomatic relations with Sung were officially opened.
翌承安3年（1173年）、清盛は答礼使を派遣し、また、後白河院からは大輪田泊までの商船通航許可を得て宋の商船に瀬戸内海を航行させ、また、後白河院が宋の使者に答物を贈ったことによって、宋とのあいだに正式に国交が開かれて日宋貿易が拡大した。