Why were the incan roads so impressive?

because the Incans had way too much swag.

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Possibly, but it is far more likely that the Incans didn't use beasts of burden and the horse didn't exist until the Spanish invaded. Information was therefore passed on knotted rope called "keepos" and was carried by runners on foot between cities. Running is faster if you are on a road than it is over bad terrain, therefore this may have been a major reason why the roads were created and maintained to such a high degree of Excellence.

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