Two main reasons Emperor Kanmu decided to transfer the capital from Heijo-kyo to Nagaoka-kyo were the geographical location of Heijo-kyo and its inconvenient water infrastructure.
桓武天皇が、平城京から長岡京へ遷都を決めた理由の一つに、平城京の地理的条件と用水インフラへ不便さにあった。