Final answer:
Belém is the city at the mouth of the Para River, serving as the 'gateway to the Amazon.' It is a critical port for distribution and international trade in the region. Manaus also plays a key role, with its free-trade zone and status as a hub for large shipping vessels.
Step-by-step explanation:
The city located at the mouth of the Para River and often referred to as the 'gateway to the Amazon' is Belém. This city is positioned as a critical link between the Atlantic Ocean and the vast interior of the Amazon Basin. Belém's strategic location has made it a significant port for the region, allowing for the distribution of goods throughout the Amazon and facilitating international trade.
Manaus, on the other hand, located further upriver, serves as another critical hub within the Amazon. It boasts a free-trade zone and a complex electronics production, alongside being a gateway for oceangoing vessels travelling up to Iquitos in Peru, thereby being a core city for economic development in the area.