Final answer:
The keystone is the central voussoir at the top of an arch or vault intersection, crucial for structural integrity in architecture, particularly noted in Gothic styles.
Step-by-step explanation:
In architecture, the is the stone at the crown of an arch or at the intersection of two or more vaulting ribs. It is the central wedge-shaped voussoir that is the last piece placed during construction and locks all the stones into position, allowing the arch to bear weight. This concept is especially prominent in the ribbed vaulting of Gothic architecture, where the keystones are not only functional but also contribute to the aesthetic and structural intricacies.
Gothic architecture often exhibits a keen interest in verticality, with features such as pointed arches, ribbed vaulting, and lancet windows that direct the viewer's gaze upwards. The ribbed vaults may feature additional structural elements, such as iron rods, to ensure stability. Noteworthy is that each vault's ribs and keystones can sometimes form complex patterns, such as lierne ribs or tierceron, which evolved into more ornate styles like the Perpendicular or International Gothic.