During the Middle Ages the Cart of St. John was a smallish cart that was used to carry a large candle in the procession from Piazza della Signoria to the Baptistery that was held on June 24th, the feast day of St. John the Baptist, patron saint of the city. Over the years the "Cart of St. John" developed into a sort of tower, which was 10 metres high, 4 metres wide, with a 3 metre base and divided into four tiers with niches to contain children, while a man dressed in skins, to impersonate the saint, stood on the top. He was usually a poor man who was paid 10 lire for this somewhat difficult job by the Guild of Merchants. From his lofty position, the man would eat, drink and distribute sweetmeats, comfits and coins to the population, stirring up a veritable brawl around the Cart: the quick wit of the Florentines rebaptised it the "brindellone", a word used to describe a tall, strong, poorly dressed and disjointed man who uses rude gestures. Although this type of cart had fallen out of use by the 18th century, its name, "Brindellone", still remains. It is now used to indicate the complicated piece of machinery that catches fire in the square between the Baptistery and the Cathedral on Easter Sunday (no longer on June 24th), freeing the doves that have taken the place of the man dressed up as St. John.

This ceremony, known as the "explosion of the Fire Cart", is also linked to another of the traditions of Christian Florence; thanks to Pazzino de' Pazzi, the city also found fame during the First Crusade (1056-1100): with sword in hand, the Florentine nobleman was apparently the first to scale the walls of Jerusalem in July 1099 and Godfrey of Bouillon rewarded him for his exploit by giving him two pieces of silica from the Holy Sepulchre (today in the church of SS. Apostoli), later used as flints for this traditional event. The sparks from the silica touched off a rocket, shaped into a dove, in the interior of the Cathedral; this flew down a wire connected to the festive Cart and set off all the firecrackers and Catherine wheels. When everything functioned as it should, farmers believed it was a good omen for the coming harvest. Nowadays the ceremony is held on Easter morning and is very popular with tourists, though the fire used to set off the mechanism is now just a simple cigarette lighter.