Grotesque as a word means “creatures of the Grotto” which stems way back before the Christian churches and refers to the sacred caves of paganism. Early churches were built over the heathen “grottos” and these delicately creepy statues and carving were incorporated on the wall and corners of the new buildings in the forms of animal gods, masques, sirens, gorgons, satyrs, serpents and other idols. These same deities were worshipped side by side with the Christian ones, so the people would continue to come to church by force of habit, finding their familiar idols there. Some hardly noticed the change, which is exactly what the early church authorities counted on. Pope Gregory the Great ordered missionaries to “accommodate the ceremonies of the Christian worship as much as possible to those of the heathen, that the people may not be much startled at the change.”
Later, the Grotesques were defined as “devils”, and the church was left with the images of rival deities undermining their religion. The people secretly prayed to them, or touched them for “luck,” and often gave offerings. The traditions of the grotesques were perpetuated by secret societies among artist, masons, and smiths, whose work together preserved the gargoyle art we still see today adorning famous buildings and ancient shrines. Above is a view from Notre Dame, Paris.
Source text; Encyclopedia of Myths and Secrets