Cornerstone

A cornerstone is a stone that is traditionally placed at a building’s foundation or corner to mark the starting point of construction and to help align the structure. In historic masonry, the cornerstone often was laid first and could bear ceremonial significance, sometimes carrying inscriptions or symbols related to the project.

In modern practice, the cornerstone is frequently ceremonial rather than structural. The laying ceremony serves as a public or commemorative event, and the stone may be inscribed with the construction date, names of sponsors or officials, and a dedicatory message. Some cornerstone stones also contain time capsules or other commemorative elements, though the actual load-bearing work is performed by other foundation components.

Etymology and origin: the term combines corner and stone, referring to its position at a corner of the building and its status as a stone. The concept has deep historical roots across cultures, and cornerstone ceremonies have long been used to mark the initiation of important public projects.

Beyond architecture, cornerstone is widely used metaphorically to denote a foundational or essential element of a system, theory, or organization. The phrase often conveys stability, continuity, and a sense of beginnings, even when the item is symbolic rather than physically required.

Related terms include foundation stone and keystone.