A cornerstone (or foundation stone or setting stone) is the first stone set in the construction of a masonry foundation. 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.
Some cornerstones include time capsules from, or engravings commemorating, the time a particular building was built.