A basket arch is an arch built up from several circular segments of differing radii, giving it the outline of an upturned basket. It is also known as a basket-handle arch or a three-centred arch, and in Dutch as a paanderboog, from paander, an old word for a basket.
How it is built up
Where a semicircular arch is a single circle with one centre, a basket arch is made up of three, five or sometimes seven segments:
- At the springing (bottom left and right) sits a segment with a small radius: the arch rises steeply, almost vertically.
- At the crown sits a segment with a large radius: that part runs almost flat.
The combination gives the basket arch a distinctly angular character at the sides and a flattened top. It differs from a true ellipse in that an ellipse has continuously changing curvature, while the basket arch is made of geometrically exact circular arcs — which meant it could be set out with compasses and string, and so could actually be built on site.
Why it was used
The advantage is purely functional: for a given span, a basket arch is much lower than a semicircular arch. That makes it well suited to:
- Stone bridges — a wide navigable opening without the deck having to sit high. A semicircular arch over 8 metres would rise 4 metres; a basket arch achieves the same width at a fraction of that height.
- Gateways and passages — a wide opening in a wall without the arch intruding into the masonry above.
- Vaults and niches — wherever the available height is limited.
The form appeared in the Gothic period and was widely used from the Renaissance onwards. The keystone of a basket arch is usually left uncarved.
Points to watch
- Greater horizontal thrust — the flatter the arch, the harder it pushes outward. The springings of a basket arch therefore need heavier resistance: thick piers, buttresses or a tie rod.
- An accurate centre — a basket arch is built on a timber centre. The transitions between the segments must be fluent, or the kink shows in the silhouette.
- Often confused with the Tudor arch — that has a pointed crown; the basket arch is flat and rounded at the top.
Related terms
- Arch
- Depressed arch
- Springing
- Keystone
- Arch bridge
- Arch centering
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