1,000 years ago in North America, long before pilgrams set foot in Massachusetts, there was once a large civilization whose city center was ringed with enormous earthen pyramids, vast farmlands, and wealthy suburbs. For hundreds of years it remained the largest city in North America - but no one knows its name.

Today, the large city that once existed in St. Louis' current footprint is called Cahokia, and its creators are commonly called the Mound Builders because of the 120 or so enormous mounds they left behind.  Shaped much like the stone pyramids of the Maya civilization to the south, these mounds rose up hundreds of feet, and were often built on top of tombs. At their summits were ceremonial buildings made from wood and thatch. Today, you can see one of the only remaining pyramids, known as Monk's Mound. 

But long before St. Louis was founded in 1764, a mysterious fire had changed everything.

A mysterious fire transformed North America's greatest city in 1170 by Annalee Newitz, io9.com