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Capstone
cap·stone [ káp st-n ] cap·stones- Plural (NOUN)
1. Top stone: a stone used at the top of a wall or another structure
2. High point: something considered the highest achievement or most important action in a series of actions
– Encarta World English Dictionary
The Cornerstone (or foundation stone) concept is derived from the first stone set in the construction of a masonry foundation, important since all other stones will be set in reference to this stone, thus determining the position of the entire structure. Over time a Cornerstone became a ceremonial masonry stone, or replica, set in a prominent location on the outside of a building, with an inscription on the stone indicating the construction dates of the building and the names of architect, builder and other significant individuals. The rite of laying a Cornerstone is an important cultural component of eastern architecture and metaphorically in sacred architecture generally.
– Cornerstone, Wikipedia
A Keystone is the wedge-shaped stone piece at the apex of a masonry vault or arch, which is the final piece placed during construction and locks all the stones into position, allowing the arch to bear weight. Although a masonry arch or vault cannot be self-supporting until the Keystone is placed, the Keystone experiences the least stress of any of the [other stones], due to its position at the apex….The term is used figuratively to refer to the central supporting element of a larger structure, such as a theory or an organization, without which the whole structure would collapse. Example: Trade is the Keystone of modern civilization.
– Keystone, Wikipedia
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