2,444km (1,519 miles) N of Rio de Janeiro, 2,468km (1,533 miles) N of São Paulo
Belém's an old city, founded in 1616 on the spot where the Amazon River reaches the sea. The first and most important building was the fort. Belém was not a commercial enterprise but a strategic investment. By controlling the mouth of the Amazon, Portugal could prevent other nations from penetrating into the vast interior, and not incidentally expand the borders of its own South American empire. Peasants and soldiers were required to feed and man the fort, along with a church and governor to keep peasants and soldiers in line. And that, give or take a tiny merchant class, was pretty much Belém for some 200 years, until in the latter half of the 1800s a Scottish engineer named Dunlop discovered vulcanized rubber, and realized it would be the perfect thing to cushion the ride on that nifty new invention, the bicycle.
Demand for rubber latex, then grown exclusively in Amazonia, soared to unimagined heights. Awash in money from rubber, Belém's unimaginative elite began importing civilization wholesale from abroad: a cast-iron market hall from Scotland; streetlights and electric trams from England; dresses and lingerie from Paris. In the copied-from-England parade ground park (now Praça da República) they built a copied-from-Italy opera house, a nice counterpoint to the copied-from-Rome basilica in the suburb of Nazaré. Everything built and bought was of the finest materials: marble, jacaranda, ebony, iron, silk, lace. Then the price of rubber crashed, and Belém never quite figured out how to bounce back. Today the city of 1.5 million survives as an export point for Amazon products.
For visitors, the chief attraction remains that 19th-century legacy. The vast Ver-o-Peso Market on the banks of the Amazon has every rainforest product imaginable available for sale. The old downtown, with its fort and cathedral and decaying stock of 19th-century buildings, provides a decent day's strolling.
Belém's cuisine is remarkable, with a mix of Amazon and seafood ingredients found nowhere else in Brazil. No visit is complete without an evening at a good Belém restaurant, and a stop at a tropical fruit-juice stand or ice-cream shop.
In a long-ago world before deforestation, the other attraction to Belém might have been the rainforest, but Pará state has chopped its forest down with such enthusiasm there's very little original forest left within easy journey of Belém.
Instead, Belém's chief wildlife attraction is the island of Marajó, the world's largest freshwater island, which sits at the mouth of the world's largest river. Occupied by buffalo ranches and prone to periodic flooding, Marajó's landscape has vast flocks of colorful wading birds, caiman, and piranha.
For visitors with limited time to spend, I'd recommend no more than a day or two in Belém and then a 3- or 4-day journey to Marajó.