Today cut down to a mere 16m, this 13th-century tower-house complex belonged to the prominent Guelph family of the Catalani (or Castellani), who had two much taller ones as well in Piazza Maggiore, both felled by an earthquake in the 15th century. There are remains of frescoes on the ground floor of this one, in a room that may have been used as a merchants' inn.
The story goes that the tower was built by Delfino Castellani to imprison his Ghibelline grandson, Alberto Carbonesi, who was in love with Virginia Galluzzi, a member of the family's arch-enemies, who was herself looked up in the even more impregnible Torre Galluzi.
Whether or not Bologna's Romeo and Juliet story is true, it is certain that one member of the family at the time, Catalano di Malavolti, was, along with Loderingo degli Andalò, a founder of the Frati Gaudenti, a military order of monks founded in Bologna in 1261 and dedicated to bringing peace to cities torn apart by rival Guelph and Ghibelline factions.
In 1266, the two new monks were invited to act as arbitrators in Florence, only to be run out of town a few months later for their lack of impartiality; Dante sent both into the Inferno (Canto XIII) with the hypocrites. Not long after, in 1280, the Torre dei Catalani was hit by lightning. The tower later perhaps served as a brothel after the original one had to be relocated for the building of the Archiginnasio; the original name of Vicolo Spirito Santo was Via del Bordello.
Vicolo Spirito Santo
Images by: Ico-Neko, Creative Commons Licence