This poor chap, Giordano Bruno, was burned at the stake for heresy during the Counter Reformation (the Holy Inquisition).
For a long time the Campo de' Fiori square was the site for public death penalties.
It has always been a site for fruit and veg markets. In fact the square's name: Campo de' Fiori means "Field of Flowers".
| About Piazza Navona and Campo de' Fiori area of Rome|