In old times, in today's Piazza del Popolo there was a poplar forest with a century-old walnut tree in the middle; under this tree the tomb of Emperor Nerone was located. Due to the presence of the grave, the area was popular among witches and necromancers who started to gather here. Around 1100 the population became intolerant and, at the end, Pope Pasquale II made an exorcism: he exhumed the skeleton of Nero and burned it together with the walnut tree. The ashes were thrown in Tevere river and a small chapel was built where there once was the tree. The name of the square might come from the latin word "populus" ("poplar") in memory of this event.