I wonder about that. The stockade (the outer one, anyhow, that they found postholes for) was about 2700 feet long, with "wattle and daub" to fill in the gaps between logs. That doesn't include defenses in or along the river, whose traces the Crawfish River would have obliterated long ago. And my own rough estimate comes up with room for more like 2-3000, though that estimate includes kids--so maybe 300 able-bodied men is reasonable.
And, pet peeve, they gave no estimates for how many people lived outside the city walls.
The mounds and stockade were built with stone tools. I'm not sure exactly how long it would take to cut down, trim, and haul the couple of thousand trees to build it. (Harder if the area was intensively used before hand, meaning they'd have to haul trees farther.) If it took a day for two men to cut/trim/haul a tree, that's about 4-5000 man-days for the stockade. You need farmers and fishermen too, so if you can spare a team of 20 to work on the job that's a couple of years of work (not in the winter or harvest time)--less than I expected. And then there's the weaving of small branches and vines, and the mud fill...
One of the mounds was a low kame that the residents built up a little, and one of the low mounds is almost completely gone. The others have been excavated and reconstructed.
They abandoned the city about the same time Cahokia was abandoned--something went sideways for the Mississippians, well before Columbus. People lived in the area for thousands of years, apparently, but the city was fairly recent. Figuring out what age the building postholes fit into is a bit tricky, especially since the area was heavily plowed for a while.
This part of the world doesn't have much in the way of ancient stone monuments.

