Trefoil arch
From Infogalactic: the planetary knowledge core
File:Rampillon Saint-Éliphe 491.JPG
Trefoil arch in the choir of the parish Church of Saint-Eliphe (13th century), Rampillon, Seine-et-Marne (Ile-de-France).
A trefoil arch -- or three-foiled cusped arch -- is an arch incorporating the shape or outline of a trefoil — three overlapping rings. It has been widely used for its symbolic significance in Christian architecture.
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