On December 13, 759, in the period of retired Empress Koken and Emperor Junnin, construction of Horanomiya was started in Omi Province because it was deeply related to the Fujiwara clan (Nakamaro's grandfather FUJIWARA no Fuhito's posthumous title was Tankaiko [Tankai means Omi], and his father FUJIWARA no Muchimaro was an Omi no kami [governor of Omi Province]) and Nakamaro himself was an Omi no kuni no kami (governor of Omi Province).
孝謙上皇と淳仁天皇の時代の759年(天平宝字3年)11月16日、藤原氏と縁が深く（仲麻呂の祖父藤原不比等は淡海公、父藤原武智麻呂は近江守）仲麻呂も近江国守であったことから、近江国に保良宮の造営が開始された。