Amazonian cities

They were living on mounds in the flood plain in the Amazon basin--well, not always flooding. Lidar shows reservoirs, so maybe it wasn't always flooded. (or maybe the reservoirs were built late, during a drought?) In fact, if they grew corn, that can't handle above 2 weeks of flood, and then only at certain times in growth. Cassava isn't fond of flooding either.

They fortified two of their towns, and some points along the causeways. Maybe outsiders, or maybe they had a history of civil war? Look at the lidar image, and imagine where wooden structures might go. People don't usually live inside fortified areas much of the time--it's crowded and unsanitary. I'm guessing that there'd have been wooden houses not far from the causeways. The image is from the above ArsTechnica article:

The group in question seems to have started going sometime around 500AD, and abandoned things about 1400AD--pre-Columbus=pre-known-epidemics. Climate change, perhaps? "This'll only last a century or so"--but technology can vanish in a generation.

The Amazonian civilizations made "geoglyphs", which were supposedly for ceremonial uses. "The count is three and two, two men on, ... and he calls time."

This is from Nature: article "articles/s41467-018-03510-7"

Unfortunately thorough excavation and analysis will probably take decades, but it should be fun to see what we learn in the meantime. I assume there was some trade across the Andes, and it looks like feathers (The influence of Amazonia on state formation in the ancient Andes It is argued that Arawak expansion in the Amazonian lowlands, completed by c. AD 500, was a prerequisite development for stimulating the rise of Andean highland empires, which were heavily dependent upon imported prestige Amazonian feathers.) might have been an important item. I wonder if it was easier to trade with the Aztecs and their precursors.