In 784 Emperor Kammu aspired to relocate the capital from Heijokyo (in current Nara) and remarked that 'the Emperor really entrusts Tanetsugu with decisions of entire internal and external matters,' so Tanetsugu advised him about transferring the national capital to Nagaoka, Otokuni District, Yamashiro Province.
784年、桓武は平城京からの遷都を望み、「天皇はなはだこれ（種継）を委任し、中外の事皆決を取る」とまで評されていた種継は、山城国乙訓郡長岡京市の地への遷都を提唱した。