Why were artificial ruins and grottoes used in 18th-century English gardens?

In 18th-century English gardens, artificial ruins and grottoes were primarily used to enhance the landscape's pictorial qualities and evoke specific emotional responses, such as solemnity, sublimity, or terror. These features were central to a style of garden design that sought to create an air of accident and surprise by incorporating elements associated with the remote in time and space.12

The use of these structures was driven by several aesthetic and philosophical motivations:

• Romanticism and Association: Influenced by Romanticism, designers aimed to arouse varied sensations in the viewer through associations with the past or exotic locations.12
• Visual Effect: Often categorized as follies, these generally nonfunctional buildings were erected to "complete" or improve a natural setting, serving as eye-catchers that added depth and character to the garden's composition.2
• Picturesque Ideals: Adherents of the Picturesque school argued that deliberately designed features—such as rocky chasms, simulated grottoes, and ivy-covered ruins—were more appropriate for a natural garden than the rigid, geometric order of earlier eras.1

Grottoes, in particular, were often constructed from fanciful arrangements of rocks, shells, and glass to mimic natural caves, which were historically regarded as dwelling places of divinities.3