Final answer:
Marco Polo dictated his far east adventures while in prison in Genoa, a rival of Venice.
Step-by-step explanation:
The city in which Marco Polo dictated his far east adventures while in prison, which was a rival of Venice, is Genoa.
Genoa, along with Venice, was one of the wealthiest city-states in Europe during the late Middle Ages. Marco Polo's travels to the East contributed to the trade links established by the city-states, and his account of the splendors of the Khan's palace became famous.