Westbound from Milwaukee, the scenery on I-94 gradually shifts from subdivision and strip malls to rolling Wisconsin prairie blanketed in cornfields.
At Exit 259, about two-thirds of the way to Madison, some make a seven-minute detour to Aztalan State Park, a tranquil rest stop on the banks of the Crawfish River.
It's a chance to see an unusual archaeological site, an outpost of a long-lost Indian civilization. Toward twilight, you can sit atop a grass-covered, 900-year ceremonial mound and take in the pastoral vistas.
And, perhaps sitting or at one of the park's picnic tables, wonder: Were they really cannibals?
In 1836, a territorial settler came across the series of earthen mounds on the west bank of the river that clearly were not the work of nature.
Surveyors and scientists followed and determined the rises were the work of a vanished pre-Columbian culture.
As the city-building Aztecs of Mexico believed they were originated in a land to the north, the mounds in Jefferson County were given an Aztec-inspired name: Aztalan.
The federal government wasn't interested in acquiring the ruins; the surface was plowed for farming and several mounds were levelled.
Two of the three large flat-topped ceremonial platform mounds - the tallest is 16 feet - remain fully intact; of the 40-some smaller "marker" mounds, nine are still present.
The first formal scientific excavation of Aztalan, in 1919, determined the perimeter of the stockade and its watch towers; underground within the enclosure were found house sites, tools, pottery shards and more.
The fire pits and refuse piles also were found to contain butchered and charred human bones and heads: It was clear that people had eaten people here.
That the Woodland tribes of southern Wisconsin had no formal cities - and no oral history mentioning Aztalan - thickened the air of mystery at the site.
Folklore and sometimes-rival archaeological theory continue to this day. This summer, the History Channel sent a crew to do an Aztalan show. On a more serious note, there were two scientific digs this summer.
The park is just 172 acres; the ancient town occupies about 17 of them in an oak-ringed swale between the highway and the Crawfish River.
Throughout the year, busloads of school children climb the lawn-topped mounds and walk around parts of the partly reconstructed stockade.
There's no interpretive ranger here, just a grounds crew. Friends of Aztalan volunteers give tours and raise funds for the site, but on your own you'll have to make do with reading signs that sketch some of the story here.
The grounds are mowed, to point up the size of major mounds. Smaller mounds outside town stockade are close to the parking area and highway.
You'll find grills at the picnic tables there.
Few know Aztalan as intimately as Robert Birmingham, who retired as official state archaeologist and is now a professor of anthropology at University of Wisconsin-Waukesha, near Milwaukee. His "Aztalan: Mysteries of an Ancient Indian Town" was published in 2006 by the Wisconsin Historical Society Press.
Here's his take: "Aztalan was the northern outpost of a great civilization comparable to other great early civilizations in the world. We call them the Mississippians; they rose after AD 1000 and had, at its centre, the first city in what is now the United States - that's Cahokia, in present-day Illinois. It was a very large city and had a society that was very complex. It was similar to Mayan cities in Mexico. They built large earthen mounds as platforms for important buildings. The major mound at Cahokia, where the ruler probably lived, is 100 feet high and greater in volume than the Great Pyramid of Egypt, though built of earth."
Birmingham said this farming society developed and expanded throughout much of Eastern North America. The Crawfish feeds into the Rock River, a tributary of the Mississippi; water transportation was the common way of getting around. The Aztalan outpost lasted perhaps 100 to 150 years.
Around the year 1200, the Mississippian civilization collapsed in the Upper Midwest, for reasons still undetermined.
One current theory points to worldwide climate change around 1200, when there was a century of drought. "Obviously, that made it harder to grow enough food for large populations," Birmingham said. "People just disbursed.
"Indigenous disease has also been brought up. When you get 20,000 people living together in poor sanitary conditions, it's ripe for epidemic. Things like tuberculosis have been found among the Mississippians."
Persistent warfare could have been a factor on the Crawfish River, he said. "The Mississippian culture was aggressive and expanding. Aztalan is one of most heavily fortified sites in the archaeological record of Eastern North America."
Birmingham's thoughts about cannibalism there are much more nuanced.
Human remains at the site - those found in 1919 and those found since - "have been analyzed and don't fit the pattern of cannibalism... at least for food," he said.
Eating others, Birmingham explained, is an ancient and worldwide consequence of intense warfare: "The taking of trophy heads, cutting up the bones of your enemies and eating them ritually - taking the power of your enemies - is well-documented in many cultures.
"In Wisconsin, the Ho-Chunks themselves recite a story in which they greeted some Illinois people who were potential enemies by killing them, putting them in a pot, then boiling and eating them. It was not for food, but to show great disdain."
The Mississippians at Aztalan, he thinks, got along with some Woodland tribes, but others would've thought these intruders from the south would've been trespassing on local land. Hence the stockade; hence warfare.
The Ho-Chunks, also known as Winnebago, are still in Wisconsin; they own six casinos. Yet there is no mention of the Aztalan people in any of their passed-down stories.
Birmingham believes this dearth of oral history may be due to so many Native Americans - 80 percent, he says - dying of disease introduced by Europeans: "It's like burning down the library."
The thousands who visit Aztalan every year include Americans and foreigners interested in pre-Columbian culture. Among them are descendants of Wisconsin's Woodland tribes: "They take pride in knowing that Native people were more sophisticated."
Aztalan, he said, also draws new-age Druids who may have read florid Aztalan articles that abound on the Internet.
In any event, Birmingham said, the site is archaeologically impressive. Cahokia, near East St. Louis, Ill, is also a state-operated historical site.
But though that town once covered six square miles, "there are subdivisions and businesses on part of the site. You can even see the St. Louis arch from there! That makes it difficult to get your head around the past. But you can stand in the middle of Aztalan and not see modern intrusions."
Especially as day comes to a close, when visitors are few, the clouds are streaked with red and an autumn mist begins to roll up from the oaks along the river.
Grab a picnic table. It's suppertime.