added by archaeologs A large island at the mouth of the Amazon River in Brazil with numerous artificial mound sites. Small one served as house platforms and larger ones contain urn burials. The pottery has sophisticated polychrome designs and is similar to that of pre-Columbian Andean cultures. Radiocarbon dates suggest that the Marajoara style began no later than the 5th century AD and lasted until 1300 AD. The largest center, Os Camutins, has 40 mounds. It is the world's largest fluvial island (one produced by sediments deposited by a stream or river) and half of it is flooded during the rainy season.