It's thought the expression 'kawakudari' (川下り) was first used when boats transported logs to help in the construction of the short-lived capital Nagaoka-kyō (長岡京 784-94).
With (a lot of) poetic license we might better translate 'kawakudari' as 'shooting the rapids'.
Kameoka (亀岡市) prospered as a port after the creation of the Sanin-dō Highway (山陰道) some time between the 7th-8thC.
Wood from the Yuge (弓削) and Yamaguni (山国) areas was sent by river through the mountains and out into the Kyōto basin via the Hozu-gawa (保津川).
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