What is the author's tone in The Travels of Marco Polo by Marco Polo?

Rustichello uses the personal pronoun "I" in narrating tales told to him by his cellmate Marco Polo. The narrator confirms that Marco Polo tells the truth and sees these things he tells Rustichello with his own eyes. This is a subjective account of an Italian romance writer from Pisa who records these tales "to occupy his time" while they are in jail. The travels are told by Marco Polo thirty years after he begins them as a seventeen year-old youth.