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It was not always possible to have a cylindrical base to support a dome. To support a dome on a square base arches could be built to bridge the corners and create an octagonal base. These were called squinches. An even more elaborate system of transferring the thrust of a dome to four points was to employ segments of vaults which are called pendentives.
© Elizabeth Rankin and Amanda Skeet, Faculty of Arts, University of Auckland, 2004.