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ThedesignThe^ dome^ of^ SantaMariadel^ Fiorerises^on1anoctagonaldrumbuilt^ in^ stoneand^penetrated^ by^ alarge^ circularwindowoneachofits^ faces.^ B
etween^the^ base^ andthe^ top,^ thereare^2fourringsor“chains”ofsandstone^ reinforced^ withiron,^ whichtogetherwithanother^ series^ of^ wooden^bands^ compress^ thewhole^and^prevent^ it^fromsplaying^ outatthe^ bottom.^ T
hedome^is^crowned^3by^ an^oculusand^4a^lantern^whoseconstruction^was^ completedin1471,^35years^ after^ therestofthe^ dome.GeometryBrunelleschi’sconstruction^follows^ thedesign^ofNeri^ di^ Fioravante,^who^ envisaged^a^ pointeddome.Theeight^ arcs^ that^ reachfromthe^ base^ofthe^ dome^ to^ apoint^ followthe^ classicalGothic^dimensionsofthe^ quinto^ acuto(pointedfifth),^inwhicha^line^ four-fifthsthe^ length^ of^ thediameterof^ thebaseisused^ to^createthe^ arc.^
The^ octagonal^base,^ separatedbystone^ ribs^atitsvertices,^wasnotbuiltprecisely,and^there^ aresome^ irregularitiesinits^ radii.Hidden^ DetailsSeveralmillion^ brickswereusedto^buildthe^ dome.^The^ terra-cottatilesonthe^ roof^ andthe^interior^plastering^ conceal^manydetails^of^theconstruction,^ but^expertscan^ tellthat^thebricks^havedifferent^ shapes^ depend-ingonwhere^they^ werelaid.Strong^ SkeletonBecause^ of^ the^ effectsofgravity,^thebaseofa^dometends^ to^ splay^outward.^ To
reducethis^ tension,^Brunelleschi^connectedthe^ inner^and^ outer^ vaultswithsolidvertical^brickarches.^ T
hejoints^ are^rein-forced^ withhorizontalrings.FERNANDO^BAPTISTA/NGS