Which architectural element is characterized by a skeletal structure of ribs?

The rib vault is characterized by its skeletal structure that includes arches, known as ribs, which support the vault. This architectural innovation allows for the distribution of weight and enables the creation of a more intricate and complex interior space, often seen in Gothic cathedrals. The ribs create a framework for the vault, which is typically constructed from lighter materials than the traditional barrel vault, allowing for larger windows and increased illumination in the space.

The presence of these ribs not only enhances structural integrity but also adds to the aesthetic detailing of the interior, allowing for variations in design and style. Rib vaulting became prominently utilized during the Gothic period, exemplifying the architectural advancements of that era.

The other options do not describe this specific characteristic: a dome, while also using an arched form, lacks the ribbed structure; an archway is a simple architectural feature that does not encompass the complexity of ribbing; and a pillar is a support structure that stands independently, typically not incorporating the concept of a vault.