A vault keystone is the closing stone at the highest point of a vault, where the vault ribs converge — the last piece of stone to be placed, which “locks” the vault into position. Vault keystones are often richly decorated with coats of arms, floral motifs or figures.
Function
- Structural — the vault keystone locks the ribs in position and makes the vault stable
- Closing piece — only once the keystone is placed can the centering (wooden formwork) be removed
- Load distribution — distributes the compressive forces from the crown evenly across the ribs
Vault keystone vs. keystone
The terms overlap:
| Term | Context |
|---|---|
| **Keystone** | The topmost stone in any arch — including a simple window or door arch |
| **Vault keystone** | Specifically the keystone in a vault, where multiple ribs converge |
A vault keystone is always a keystone, but not every keystone is a vault keystone.
Decoration
Vault keystones are often the most elaborately decorated element in a vault:
- Coats of arms — of the patron or diocese
- Floral motifs — rosettes, foliage
- Heads or figures — saints, angels, mythical creatures
- Painting — often polychrome (multicoloured)
Identification
In a church or historic building, you can find the vault keystone by looking up at the point where the vault ribs converge. The round or polygonal ornamental piece at that junction is the vault keystone.
Restoration
When restoring a damaged vault keystone:
- Use original stone types (natural stone or brick)
- Have decorated keystones restored by a stone mason
- Never remove a vault keystone — the structure will become unstable
Related terms
- Vault
- Vault rib
- Vault web
- Keystone
- Springing point