Voussoir
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A voussoir is a wedge-shaped element, typically a stone, which is used in building an arch or vault.
William Henry Playfair, University of Edinburgh: bevelled edges of each stone block emphasise the voussoirs, which have a curved base and together form a semi-circle at the top of each arch.
Joggled voussoir arch, located at the Mausoleum of Theodoric in Ravenna, Italy. (520 CE)
Keystone arch, Italian courtyard, 16th-century late Renaissance (Mannerism).
A single voussoir unit, made of marble, 6 5/8 x 14 1/2 in. (16.8 x 36.8 cm) 1130–40.
Joggle (architecture)
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A joggle is a joint or projection that interlocks blocks. Often joggles are semicircular and knob-shaped, so joggled stones have a jigsaw- or zigzag-like pattern.
Voussoir
…depending on the type of arch being constructed—round, pointed, horseshoe, multifoil (which require voussoirs to be cut at different angles), and joggled. Joggled voussoirs were originally developed in Roman architecture to strengthen the structure, before being implemented in Islamic architecture. The wedged…
Joggling above a window lintel of the Damascus Gate, Jerusalem