It’s called Cahokia now.

But that’s not its real name.

We just don’t know what the inhabitants of Cahokia called their city when it was the largest metropolis in the Western Hemisphere north of Mexico — a city as large as London, on the other side of the Atlantic, was at the same time.

So modern historians, anthropologists and archeologists named it for a later nomadic North American tribe that moved into the same middle Mississippi region hundreds of years after the great, unknown native city reached its peak, died — and became lost to human memory.

That was a millennium ago, centuries before Christopher Columbus came sniffing around the eastern edges of this very big and very mysterious continent.

A thousand years ago, Cahokia was as vast and complex an urban setting as anything the Aztecs, Mayans or Incas built further south, with thousands of homes, hundreds of public buildings and pyramids rising 10 stories above huge ceremonial plazas and Stonehenge-like astronomical structures.

And then there was the little matter of human sacrifice, but we’ll get into that later.

So why do we know so much about the Aztecs’ golden cities, the Mayans’ pyramids and the Incas’ mountain fortresses while we know so little about a contemporary civilization much closer to us?

Building materials, baby.

The Aztecs, Maya and Incas built in stone (and some metal), so the ruins of their cities and temples remained fairly much intact (apart from the plundered gold artwork) long after their empires died.

Cahokia, on the other hand, was built with the materials at hand on the Mississippi floodplain: Earth and wood.

The constructions were just as gigantic and just as sophisticated as anything built further south, but when Cahokia died, nature took its course: Instead of ruins of carved stone, Cahokia’s edifices were slowly reduced to rounded hills and rotted post holes.

For whatever reason — war, disease, famine, societal breakdown, natural catastrophe, climate change, maybe a combination of several — Cahokia’s centuries-long golden period came to a rather abrupt end before 1400 and its people dispersed to the winds. Much the way small, functional groups of survivors will abandon the shells of non-working 21st or 22nd Century disaster cities to find spaces more suitable for the protection and feeding of small survival clans.

It would be two hundred years before a new native people, the nomadic Cahokia (from whence the site has derived its current name) of the Illinois confederacy, resettled the land where the great city had stood. And it would be another century after that before Europeans began popping up.

By that time, Cahokia’s pyramids had subsided into rounded, scrub-covered hillocks, the wooden temples and lodge houses had rotted and crumbled and the huge, painted poles of “Woodhenge” calendar circles were just ochre-coloured depressions in the earth.

So I guess it’s no wonder that early European and American settlers and their descendants didn’t recognize the remains of a lost civilization as they ploughed fields through giant public ceremonial squares and levelled enormous earthen pyramids for landfill.

New cities grew up nearby — St. Louis, across the river in Missouri, and (pretty much on top of Cahokia) East St. Louis and Collinsville in  Illinois.

Although some astute local amateur scientists and historians began to suspect there was something very special about the area in the 19th Century, they didn’t have the clout to stand in the way of progress.

The biggest block to understanding Cahokia was the built-in ethnocentric bias that 19th Century Americans and Canadians had (and which we still carry to a large extent in the 21st Century) that pre-Columbian native North Americans were rootless nomads, living off the fickle bounty of the earth in relatively small migratory groups usually numbering no more than hundreds unless brought together in their thousands for war or celebration — and then for very short periods of time.

The idea that those simple-living, wandering natives would — or even could — build huge, permanent urban communities with complex, sophisticated social, cultural and trade patterns that survived and flourished in one place over hundreds and hundreds of years was beyond the comprehension of most people 100 years ago.

The biggest of the pyramid mounds, known as Monks Mound, was protected as a small state park in 1925 and very haphazard excavations were dug on about 20 surrounding mounds, but still no one really understood the extent and the grandeur of the history buried beneath their feet and in the hillsides surrounding them.

That protected mound was not called Monks because it was the centre of Cahokia’s prehistoric religious and ceremonial life, but because a group of proselytizing Catholic missionaries set up a monastery on top of it in the 1700s. That’s history for you.

So as late as 1931, Cahokia’s second-largest mound was levelled. Through the 1940s and ’50s, farm fields gave way to suburbs, an airport was built, streets and highways ran hither and yon across the 4,000-acre (1,600-hectar) hidden cityscape. Even as late as the 1970s, a soft-core porn drive-in theatre was occupying land where once stood the greatest urban civilization north of Mexico City.

Cahokia’s big break came as the result of a massive 20th Century building project — the construction of the U.S. Interstate highway system ordered by the Eisenhower administration in the 1950s (in large part a Cold War defence plan to enable the rapid movement of large numbers of troops and weapons and to supply nuclear bombers with ready-made runways anywhere in the continental United States).

Tied in to the funding for construction of the highway system was a tidy little add-on that covered the cost of archeological study of any interesting historical areas unearthed in the construction process.

This was especially fortuitous in the case of Cahokia, the exact spot where East-West Interstate 70 (from Maryland to Utah) and North-South Interstate 55 (from Chicago to New Orleans) were about to crash into each other.

The initial construction ground prep in the area turned up so much interesting, sophisticated pre-Columbian evidence that archeologists flocked to the area to find the metaphorical gold buried in them thar hillocks.

As a result, the small Monks Mound State Park was expanded to become Cahokia Mounds State Park in 1964 and the area was designated a U.S. National Historic Landmark. In 1982, UNESCO declared the area a World Heritage Site.

Interstate 55 and Interstate 70 now follow the same patch of asphalt through that area, but if you look at a map you’ll see US 255 — the original route of Interstate 55 — suddenly takes a big swing to the east around the present state park, saved just before it became a highway interchange.

More and more of the original city site was acquired for the park, bungalows and strip malls were removed, proper excavations revealed more and more of the form and outline of the ancient city, and slowly the lost city of Cahokia was found again.

Cahokia Mounds State Park now covers about 2,200 acres (8.9 square km), about half the original settlement area but including all of the important central district where the state, religious, cultural, social, sport, manufacturing and commercial life of the metropolis was carried on.

Of the roughly 120 mounds built there by humans, 80 still survive, although — as I said before — 20 of them were badly butchered by hack explorers in the 1920s, destroying much of their archeological value. But there is still much to find: A rough estimate is that only about 1% of Cahokia has been archeologically processed so far.

So who lived there, how did this fabulous city explode into existence, how did it function and why, and how and why did it fall apart just as rapidly as it rose?

Scientists and historians have some concrete information, but much of what they believe happened is a swirl of conflicting theories based on how individual archeologists, anthropologists and academics interpret the evidence left in and on the ground.

Here’s a quick outline of what we know for sure:

Cahokia existed as an occupied, functioning centre of human activity from about 800 AD to about 1400 AD — roughly the period we call the Middle Ages in European history.

After a solid but relatively modest start, Cahokia’s population started burgeoning between 900 and 1000 AD. For the next 200 years after that — roughly the time period in which the European and the Muslim worlds were preoccupied with the Crusades — Cahokia was the centre of a North American trading empire that stretched from the Great Lakes in the north down the Mississippi to the Gulf Coast of Texas, Louisiana and Florida, and from North Carolina in the east to Oklahoma and the Dakotas in the west.

Then there was a period of rapid decline about 1300 AD and the once-great city-state was completely abandoned by about 1400 — a century before Columbus supposedly “discovered” America.

There is debate among scholars about just how many people lived in Cahokia but we know it was in the tens of thousands. Estimates run from as low as 10,000 to as high as 40,000. But the most reliable, sensible analyses put the population at around 20,000 to 25,000 people in the main city during its peak period.

That would make it equivalent in population at the same time to London, England, when London got its first Lord Mayor, Henry Fitz-Ailwyn, in 1189.

There were thousands and thousands more people living in satellite mound cities around the central metropolis and in hundreds of small farming villages that provided the bulk of the food that supplied the urban centres.

We are fairly certain that the big population boom in the 900-1000 AD period coincides with the arrival of corn seed and related farming techniques and technology from the other highly developed native empires then flourishing in Mexico and Central America.

Suddenly there was a vast, basic, reliable food supply to allow population growth and concentration and enough surplus to fuel the large trade network that flowed outward from Cahokia along the Mississippi, Missouri and Illinois Rivers.

Archeologists have found metal-working shops in Cahokia with copper from near Lake Superior, while other artisans worked with top-grade flint from Oklahoma, mica from North Carolina and seashells from the Gulf of Mexico.

The other materials had many utilitarian uses, but the carved and patterned shells — often strung together as beads —  were almost exclusively decorative and symbolic — in many ways becoming the financial currency of Cahokia.

As Cahokia’s trade expanded, so too did its cultural, social and political reach. There are more than 50 known mound-city sites scattered around the central and south-eastern U.S. today, outposts of trade and culture linked like nerve endings to the mother city, the brains of the operation.

We also know that — like the Aztecs, Maya and Incas — Cahokian society was very strict and stratified, with a top layer of intermingled nobility and religious leaders supported by military, administrative and religious castes, then traders and artisans, followed by farmers and self-employed workers. At the bottom of the pile was the vast pool of nobodies who did all the drudge work that built the great city and made it run.

What we don’t know for sure is if there was one dominant overlord — a king — and if that civic, religious and military lordship was hereditary, power passed down from one generation to the next (unless usurped).

Most historians simply refer to Cahokia as “a complex chiefdom society” because we know there was generally a big kahuna of some kind running the show — we just don’t know how he was chosen (or chose himself) and whether there was a well-defined, institutionalized code for how that chief applied and/or delegated power.

The best insight into this “chiefdom” society comes from Mound 72, a royal burial mound with some very notable finds from the 950-1000 AD period, just about the time Cahokia was hitting its robust, expansionist stride.

About 280 skeletons have found in Mound 72 but the key discovery there is the burial site of a most noble figure — perhaps the charismatic leader who was responsible for Cahokia’s sudden explosion into greatness.

The noble — probably royal — skeleton is of a man in his 40s laid on a bed of 20,000 of the valuable decorative shell discs designed in the shape of a falcon, so the man’s head is beside and on top of the bird’s head and the wings protrude from beneath his arms while the tail feathers  show between his legs. The icon of the birdman or falcon warrior is apparently a very strong and evocative religious image from ancient Mississippian culture. It is pretty much around the world, for that matter, so who knows where the idea originated and how it spread. Maybe it’s just an image so powerfully and deeply embedded in the human psyche that it’s there within us everywhere we have existed.

Nearby is a cache of 800 sharply chiselled arrowheads, divided into four separate groups identifiable as coming from the eastern, northern, western and southern portions of Cahokia’s trading empire.

Ah, money and weapons, like always. So what about the servants unto death and the sacrificial maidens? Yep, they’re there too.

Adjacent to the dead chief/noble/king are the skeletons of four young men — minus their heads and hands. I’m not sure what they could do for their master in the great beyond without heads and hands but maybe they were his funary attendants: If the corpse was carried on their shoulders while they walked into eternity, they wouldn’t need heads or hands. Who knows, but it’s something along those lines, I imagine.

And then the sacrificial maidens.

In an adjoining grave, neatly stacked in rows and layers, are the skeletons of 53 young women, in their late teens and early 20s. By the evident crushing of neck vertebrae, they all appear to have been strangled in a ritualized mass execution before being placed as companions, I suppose, with the dead falcon king.

One more mass grave was found nearby — and from approximately the same time period — which may or may not be directly linked to the burial of the birdman.

This mass grave contains the tangled skeletons of about 40 men and women who seem to have died violently and been roughly cast into a pit. The positioning of some corpses — the final paralyzed activities of their heads, hands and legs — indicates at least some of these people were still alive when buried.

So is this more ritual sacrifice for the birdman chief/king/transitional god figure? Or is this evidence of a separate brutally suppressed rebellion or opposition liquidation from around the same time? Is this perhaps the extended family of the birdman unwillingly forced to go with him or is it a revenge slaying of the kith and kin of a rival responsible for the noble birdman’s death? Your guess is as good as — or probably better — than mine.

So let’s take a look at the civilized city where these barbaric acts took place.

Cahokia was big, roughly a diamond shape in layout, about 8 km deep and 2 km at its widest point, so I’m told: It just looks like a big blob to me.

The city was divided into different zones for different functions: living quarters, specialized activities like workshops and storage facilities, and public ceremonial areas.

The centre of this beehive of human activity and ambition was a palisaded central court area that included the Monks Mound and a huge plaza the size of about 45 NFL football fields spreading out before it.  Ringing that ceremonial plaza inside the wooden palisade walls were about a dozen smaller mounds and scores of buildings, all of which would be related to the ceremonial, religious and administrative life of the city and its elite.

The Monks Mound is enormous, larger at its base than the Great Pyramid of Egypt. It would have taken thousands of workers decades to build that mound, carrying the earth in woven baskets. Better minds than mine have estimated it would have taken about 14 million basket-loads of earth to build that mound 10 storeys high.

Then, sitting on top of the mound, was a 5,000-square foot building rising the equivalent of another five storeys. This was the very heart of Cahokia. This was where absolute religious, political and military power resided in the empire.

The temple/palace atop the mound was positioned in such a way facing west that, at the solstice and equinox when the sun rose due east, it would appear to rise directly out of the top of Monks Mound itself.

Spreading out in front of Monks Mound, the grand plaza had ceremonial sites (for ritual human sacrifice?), sporting fields and some of the many astronomical pole configurations — “Woodhenges” as they are called now — with which human activities could be correlated with the activities of the heavens.

There were other Woodhenges and public spaces elsewhere in the city, but this central complex was the nexus of the Cahokia empire. And from the top of Monks Mound the Cahokian elite could survey their vast domain up and down the Mississippi.

It has been suggested that the complex, ongoing programme of public construction that occupied much of the time and effort of Cahokia residents was a self-perpetuating cycle with no real purpose except to make the elite designers-overseers seem important and necessary and to accustom the seething masses to obeying orders blindly on the assumption that they simply did not understand the “big picture” their betters were implementing. Maybe yes, maybe no. The rebel in me says yes, the realist says no.

Like all good — and some bad — things, this fabulous, busy empire on the Mississippi came to an end.

In 1200, Cahokia was still the centre of a vast, complex, vibrant trading and cultural empire. By 1300, the decline had begun in a serious way and by 1400 Cahokia was a ghost city, given back to the natural elements from which it had been built. The humans were gone.

As I said before, it is uncertain what caused the demise of this great North American city. It was probably the culmination of a number of factors with a few crisis tipping points.

One thing we know for certain is the “Little Ice Age” — a very cold period lasting several hundred years which also had major effects on Europe — began about the time of Cahokia’s initial decline. If corn production was disrupted by those climatic changes, then the massive food supply a large, complex centre like Cahokia required would no longer be reliable. Shortages, then starvation, then factional fighting, then disintegration and dispersal would likely follow.

There also seemed to be increasing threat and/or conflict hanging over Cahokia during the century of decline. Archeologists have found the remnants of a number of protective stockades built and rebuilt in the 1175-1275 period, which means Cahokia was under attack — either by external enemies or the ruling elite was under attack by internal opposition. No one knows for sure, although there’s a theory for every taste out there now.

But the bottom line is that, not unlike Camelot, once there was a Cahokia.

Even if we don’t know its real name, this grand, triumphant metropolis was a city of riches, culture and knowledge existing on the banks of the Mississippi River for centuries before Christopher Columbus, in his tiny, leaking bobble-boats, drifted into the Caribbean and proclaimed it Asia (a belief Chris firmly held until his death).

Hail Cahokia. Goodbye Columbus.