In the Middle Ages, Smithfield--"a smooth field" to the north of London's walls--was a natural place for jousts, tournaments, and the selling and butchering of livestock.
Conveniently (!), animal waste from the market could be dumped into the River Fleet, which flowed into the Thames. It’s original origins as a place where livestock could be bought and sold, can be seen in the vestiges of its street names (e.g. Cow lane, Cock lane).
Public torture: Over the centuries, many criminals—particularly those accused of treason—were tortured. One of the most famous was William Wallace (“Braveheart”)- - a twelfth century hero of the Scottish people. Drawing and quartered was the preferred method, and perhaps castrated as well (but studio executives probably thought movie audiences couldn’t stomach Mel Gibson undergoing that particular humiliation.)
[Interesting side note: According to John Foxe’s Book of Martyrs, the “Marian Martyrs” would ask that their hands not be bound and their wood pile would consist of the greenest wood, so that their plaintive laments and prayers would last longer.)
The burnings of these men and women were collectively referred to as “The Smithfield Fires.”
Check out this advertisement for the entertainment to be had at the “Plow Music Booth” in 16xx:
Underlying this bill, however a real fear of disease and pollution that seemed to occur whenever so many people were brought in such close proximity. King Charles I tried to cease the Fair on several occasions during his reign. In 1637, he issued a proclamation for putting off the Bartholomew Fair, and a similar fair in Southwark:
This was only a temporary halt to such festivities; only Cromwell was able to completely stop the fun. The Fair, like all other such festivals, was banned under his regime, only to be restored in 1666 with the Restoration of the fun-loving Charles II.
But like the River Fleet, the Smithfield grounds are another part of secret London.