Arches and domes

To classify a structure, find what is solid all through, what is a frame of parts joined together, and what is a thin outer skin. Decide which describes each example and give your reason.

The record on the keel arch reports that in the qibla-arcade dome of al-Azhar, from the reign of al-Hafiz, the dome rests on keel arches over antique columns braced by wooden tie-beams ². Yeomans sees these features as defining Fatimid structure, much lighter than the solid brick piers of Tulunid building ². The chahartaq is a square domed chamber rising on four crossing arches ³; Rezavi's earliest Mughal example is the Kabuli Bagh Mosque, built by Babur at Panipat (c. 1527), where the chahartaq covers the central nave ⁴. The records describe and do not classify; the classifying is yours.

Yeomans sees the keel arches, antique columns and wooden tie-beams of the al-Azhar dome as much lighter than solid brick piers ². If you classified that dome as a solid, frame or shell structure, which part of Yeomans's description would you rely on, and why?

• The chahartaq: a square domed chamber on four crossing arches, and how it spread under the Mughals.
• The keel arch: a pointed arch shaped like an upturned boat, from Fatimid Cairo onward.
• Al-Azhar Mosque: the mosque whose qibla-arcade dome the keel-arch record describes.
• The Kabuli Bagh Mosque: Babur's mosque at Panipat, where the record says the chahartaq covers the central nave.