When the first Portuguese settlers arrived in Belém, they did not realize the Amazon River behind them was the world's largest, but they were well aware of the unique spices that natives traded down its banks, and sought to assert themselves as the gatekeepers of these niche goods with the outside world. In the late 19th century, the rulers of Belém became the gatekeepers of something much more valuable: Rubber. City officials soon lived like kings, with Belém becoming rich enough to afford luxuries equaling those of Paris and Berlin, even as the Pará state surrounding it remained the poorest in the country. The rubber boom did not last forever, and while many ostentatious monuments to the city's wealth still stand, alongside them are expansive slums, as hundreds of thousands of people now look to the city for work.