There are various theories why Shigaraki became a capital even though it was too deep in the mountains one that he was connected to the Fujiwara clan including FUJIWARA no Nakamaro in opposition to the Tachibana clan that had their base around Kunikyo; the Emperor selected Shigaraki in accordance with the advice from monks such as Roben (Ryoben) or Gyoki in pursuit of his own base of faith for Buddhism.
紫香楽の地は、当時の感覚においては余りに山奥である事から、ここを都としたことを巡っては諸説があり、恭仁京周辺に根拠を持つ橘氏に対抗して藤原仲麻呂ら藤原氏に関与したとする説や天皇が自らの仏教信仰の拠点を求めて良弁・行基などの僧侶の助言を受けて選定したとする説などがある。