In terms of diversity, America's first city wasn't that different (relatively speaking) than America's largest city, New York City, according to a new study that analyzed the teeth samples from the inhabitants of ancient Cahokia, National Geographic reported.

Cahokia was established in an area near St. Louis, Missouri by Native Americans around 1050 A.D. Fifty years later, it supported a population of 20,000 inhabitants covering a space of 5.5 square miles -- with many more citizens occupying lands in its sprawl. Some researchers believe most of the growth came from within the city, though a larger portion believes its rapid rise was due to mass immigration. Cahokia, like New York City and the greater United States, was a melting pot.

"All of a sudden, there's a giant rise in the size of the site," study researcher Philip Slater, a doctoral candidate at the University of Illinois, told Live Science.

"It contained more than two hundred earthen mounds, including the largest mound in North America, Monks Mound," said Thomas Emerson, the director of the Illinois State Archaeological Survey. "Many of these mounds were topped by temples or the houses of the elites and were arranged around large ceremonial plazas where great community political, social and religious events were held."

The recent work of Slater, Emerson, and others proved that at least one third of Cahokia's inhabitants were from other parts of the world, though they can't yet pinpoint exactly where. The process by which they identified immigrants -- matching an element found in their teeth to the type found in Cahokia -- only revealed if specimens were or were not from the area. Also muddling the picture was the fact that their methods were only accurate for individuals 18 or younger. Since they still had traces of their infant teeth, researchers were able to note if their earlier set of teeth came from one area and if their later set of teeth came from somewhere else -- something they couldn't compute for adult teeth. That's why Emerson and Slater use the qualifier at least. Only giving birth can increase a population within. Thus, adults that contributed to the population increase must have either been parents or immigrants for which the researchers couldn't account.

According to an interview with Nat Geo, Emerson said they should have a better idea of where immigrants were coming from in a few years.