Umberto Eco's (On Ugliness) is a comprehensive exploration of how the concept of "ugly" has evolved from ancient times to the modern era. Rather than viewing ugliness as just the absence of beauty, Eco argues that it is a rich, complex phenomenon deeply tied to cultural fears, moral values, and artistic expression. Core Themes and Concepts

: Ugliness was associated with a lack of harmony and moral failure.

Umberto Eco on the Elusive Concept of Ugliness - Literary Hub

: Objects or beings that provoke an immediate, visceral reaction of disgust or repulsion, such as organic decay or excrement.