The tradition, back in the Middle Ages, people believed that church bell towers were particularly vulnerable to invasion by evil spirits (maybe because the towers were often getting struck by lightning or falling down). So a tradition began of putting some kind of protective sculptural image on the towers. Some bell towers have benevolent images like saints or angels, but others have grotesque images. Those were designed The ward off evil spirits and animals and against the influence evil uses.
A grotesque images, Campanile Santa Margherita
At the doors of the towers, the grotesque images had to be carved in the keystone of the arch and doorposts. The image is also known as mascherini or scacciadiavalo. Other common decorative motifs are fleshless heads of cattle, scope are night birds.
John Ruskin was so adversely affected by them to say that in this grotesque images inhuman laughter of lascivious and brutal, too disgusting to be drawn or described, there is all the degradation in which Venice is falling.
If Ruskin is paying attention scacciadiavalo in his book ‘The Stones of Venice’. The chapter that is deals with the Grotesque Renaissance, Ruskin seems to be unimpressed with Early and High Renaissance styles, he is thoroughly disgusted by the third stage, “The Grotesque Renaissance,” his term for what is today know as the Baroque. Here, he feels architecture has lost all of the moral character he had described so eloquently in his earlier discussions on arches, and has instead been turned into the “perpetuation in stone of the ribaldries of drunkenness” and self-indulgence. This stage receives its name from the incorporation of grotesque elements, or distorted and ugly faces and bodies, often with protruding tongues, displayed on buildings and bridges. Ruskin makes a point to distinguish this “false grotesque” from the previous “true” version seen in the Gothic period, with the use of gargoyles and other distorted figures. He illustrates each of these versions in his drawing “Noble and Ignoble Grotesque,” found in the third volume of The Stones of Venice. In contrast to the earlier type, ignoble grotesque is an example of human imagination run amuck, as it steps out of the bounds of stable, organized renderings into images of the basest forms of debauchery and instability.
John Ruskin, The stones of venice, volume II – sea-story