Arcade: round against pointed
A run of arches on piers or columns. With unequal spans, round arches rise to unequal crowns; pointed arches can all reach one height.
The rules it illustrates
Pointed arches reach any height on any span. A round arch must rise half its span, so arches of different spans on one springing line have crowns at different heights. A pointed arch can be given any rise at least half its span, so arches of different widths can all be made to reach the same height.
Every arch is first built on a frame. An arch cannot support itself until it is complete. Build it on a timber centring shaped to the intrados, strike the centring only when the keystone is set and the mortar has taken, and reuse it from bay to bay, which is one reason to keep the spans of an arcade equal.
Make the end piers of an arcade the strongest. In a row of arches the thrusts of neighbouring arches cancel over each intermediate pier, which may therefore be slender; at the ends of the row nothing balances them, so the outermost piers must be made wider or buttressed.
Where it appears in the book
In the styles Romanesque.
In the chapters The Arch.