From approximately 400 BC to 1600 AD, Marajó was the site of an advanced Pre-Columbian society called the Marajoara culture, which may have numbered more than 100,000 people at its peak.

Today, the island is known for its large water buffalo population, as well as the pororoca tidal bore periodically exhibited by high tides overcoming the usual complex hydrodynamic interactions in the surrounding rivers.

[3] Large parts of the islands are flooded during the rainy season because of higher water levels of the rivers along the coast and heavy rainfall in the interior.

The island is known for the pororoca, a tidal bore phenomenon in the river that creates large waves reaching 4 m (13 ft) in height.

[4] This is also the location of Lake Arari, which has an area of 400 square kilometres (150 sq mi), but shrinks by 80% during the dry season.

Based on fieldwork in the 1940s and 1950s, the archaeologist Betty Meggers initially argued that the Marajoara culture had been founded by emigrants from the Andes and that the society steadily declined until its final collapse at approximately 1400 AD, due to the Marajó's poor soil fertility and other environmental factors.

According to Roosevelt, the Marajoara culture developed independently within the Amazon and featured both intensive subsistence agriculture and major public works.

[8] The population lived in homes with tamped earth floors, organized themselves into matrilineal clans, and divided tasks by sex, age, and skill level.

[9] In contrast, however, during the 1918–1919 pandemic worldwide of Spanish influenza, Marajó was the only major populated area not to have any documented cases of the illness.