Nagaoka-kyo was established full of hope but lasted just for ten years.
In 794 AD the capital was suddenly relocated to Heian-kyo.
Even for such a short period of ten years there was considerable construction.
We can conclude that the end of Nagaoka kyo indicates an abnormal situation.
There are many theories.
One is that many of Emperor Kanmu's relatives died there and he wanted to escape from the bad luck he thought to be at the place.
Another is that it was because of the flood of the Obata river, Koizumi river and Katsura river.
Yet a third is that the size of Nagaoka-kyo had already become so large that he could not afford to continue building.
For whatever reason it was decided to relocate the capital.