the.com/keystone arch
The brick that gets all the credit for holding up a fight it's actually in with gravity, forever.
means An arch made of wedge-shaped blocks (voussoirs) with a central top stone, the keystone, that locks all the other pieces in place by converting downward weight into outward and sideways thrust along the curve.
from From 'key' in its old sense of 'the piece that fastens or locks something shut' (as in a key locking a door) plus 'stone,' describing the wedge-shaped block set last into the crown of an arch. The engineering idea is ancient — Mesopotamian, Etruscan, and especially Roman builders mastered true arch construction — but the English compound 'keystone' itself is a later label, first applied to architecture and soon borrowed for anything indispensable, like a 'keystone species' or a 'keystone argument.'
- the trick
- compression pushes outward, arch pushes back equally
- the irony
- removing keystone fast can leave arch standing
- the age
- romans popularized it, aqueducts still standing 2000 years later
- the metaphor
- became slang for indispensable person or piece