Somewhere on the basement level or first floor of the Bulfinch Building is the hospital’s cornerstone, which was laid in a ceremony led by the Freemasons’ Grand Master Francis J. Oliver on July 4, 1818. Once the symbolically important first stone laid in a new building, cornerstones have retained their symbolism but are no longer always the first stone, and not necessarily in a building’s corner. While the hospital has documents describing the 1818 ceremony, they don’t include a description of the location, and the engraved stone has since been painted over or enclosed behind a wall. Its location is a mystery.