Look seven stories up and you’ll be amazed by a central architectural feature of Gothic cathedrals, the vaulted ceiling, which transmits the weight of the roof and walls across delicate ribs and down the heavy trunks of stone piers.

Washington National Cathedral displays a range of vault styles, from simple barrel and groin vaults in the crypt to elaborate fan vaulting in Children’s Chapel. Such elements enabled Gothic cathedrals to be constructed to greater heights than ever before, with thinner walls and tall stained glass windows.

In the Cathedral’s spectacular vaulted ceiling, round boss stones are key structural and decorative elements. Without these key load-bearing stones, the massive weight of the ceiling could not be suspended for such immense spans. Across the Cathedral, there are some 762 boss stones (the largest weighs 5 tons), and only the 14th-century cathedral in Norwich, England, has more carved boss stones.

Starting in the west end and working toward the High Altar at the east end, the boss stones depict theological statements from the Nicene Creed and Apostles’ Creed, staring with “I believe in God the Father Almighty” and ending with “I believe in the life of the world to come.” Just as the stones provide the structural support for the sacred space, the statements on those keystones reflect the theological backbone of the Cathedral.