The domes of the earlier mosques in Cairo were built on the model of Sta Sophia, with windows pierced round the base of the dome and external buttresses between them; these domes were all built in brick coated over with cement or stucco. At a later date, and when built in stone, the upper portion was raised in height and terminated with a point on which a finial was placed. These are the domes inside and outside Cairo, which are carved with an infinity of geometrical patterns interwoven with conventional floral decoration. The upper portion of the dome is very thin, so that there is little weight and comparatively no thrust, and it is to these facts that we probably owe their preservation.
In India, in the “great mosque” of Jama Masjid (a.d. 1560) and the Gol Gumbaz, or tomb of Mahommed Adil Shah (a.d. 1630) at Bijapur, the domes are carried on pendentives consisting of arches crossing one another and projecting inwards, and their weight counteracts any thrust there may be in the dome. It is possibly for a similar reason that in the Jama Masjid of Shah Jahan at Delhi (1632-1638) and the Taj Mahal (a.d. 1630) the domes assume a bulbous form, the increased thickness of the dome below the haunches by its weight served as a counterpoise to any thrust the upper part of the dome might exert. The form is not much to be admired, and when exaggerated, as it is in the churches of Russia, where it was introduced by the Tatars, at times it became monstrous.
From these we pass to the domes of Périgord and La Charente, the earliest of which date from the commencement of the 11th century. Of the western dome of St Étienne at Périgueux (a.d. 14) only the pendentives remain, sufficient, however, with later examples, to show that these French domes were different from the Byzantine both in construction and form. The pendentives are built on horizontal courses of stone, and the voussoirs of the pointed arches which carried them form part of the pendentives; a few feet above the top of the arches is a moulding and a ledge, above which the dome, ovoid in section, is built. The principal examples following St Étienne are those of S. Jean-de-Cole, Cahors, Souillac, Solignac, Angoulême, Fontevrault, and lastly St Front at Périgueux, built about 1150, in imitation of St Mark’s at Venice. The domes of the latter church were introduced into the old basilica about 1063, and were based on the church of the Apostles at Constantinople, which was pulled down in the 15th century, so that we have only the clear description of Procopius to go by. The domes over the north and south transepts and the choir of St Mark’s are smaller than those over the nave and crossing, because they had to be fitted in between more ancient structures. The construction of the domes of St Mark’s is not known, but at St Front the general design only was copied, and they built them in the Périgordian manner. The masons from Périgord are also responsible for the domes of the Crusaders’ churches in Palestine and for some of the early churches still remaining in Cyprus. The domes of San Cyriaco at Ancona and Sant’ Antonio at Padua were based upon those of St Mark’s at Venice.
In central Italy we have the dome (elliptical in plan) of the cathedral of Pisa, and it was a favourite feature over the crossing of the churches throughout Italy, being generally carried on squinch pendentives. The domes of the baptisteries of Florence, Parma, Trieste and Piacenza, are only internal, being enclosed with vertical walls and a sloping roof. In Sicily, on account of the strong Saracenic influence, the squinches are simple versions of the stalactite pendentives described under [Architecture]: Mahommedan (q.v.), the earliest example being found in the church of San Giovanni-dei-Leprosi (a.d. 1072), all the domes being ovoid in section.
Except in Périgord and La Charente, domes are not found in the churches in France, but in Spain they were introduced over the crossing at Burgos, Tarragona and Salamanca cathedrals, and were made architectural features externally. This is rarely found in Germany, for although in the cathedrals of Worms, Spires and Mainz, and in the churches of St Martin and Sankt Maria im Capitol at Cologne, the crossings are covered by domes, always carried on squinch pendentives, externally they built lanterns round them.
In the Renaissance styles, the dome was at once accepted as the principal characteristic feature, and its erection over the crossing of Santa Maria del Fiore at Florence was the first important work entrusted to Brunelleschi. The dome was begun in 1422, and finished in 1431, with the exception of the lantern, begun the year of his death in 1444, and completed in 1471. The dome, which is octagonal on plan, is 139 ft. in diameter, and is built with an inner and outer casing, concentric one with the other, tied together by ribs between them: the lower portion is stone, the upper part is brick.
The double shell was also employed by Michelangelo in the dome of St Peter’s at Rome, the outer shell being raised higher than the lower and connected by ribs one with the other. The diameter is 140 ft. and the construction in brick, similar to that at Florence, but the ribs are in stone from Tivoli. In both these cases the weight of the lantern was a very important consideration, and is responsible for the repeated repairs required and the introduction of additional ties.
In this respect Sir Christopher Wren solved the difficulty at St Paul’s cathedral, London, in another way: he provided three shells, the lower one with an eye in the centre forming the inner dome as seen from the interior; the middle one of conical form, and the outer one framed in timber and covered with lead. The conical shell carries the lantern, the weight of which is carried direct to the base, bound with iron ties, with such additional strength as may be given by the portico round.
In all these cases these domes are built on lofty drums, so that externally they present quite a different appearance to those of the Pantheon at Rome, or Sta Sophia in Constantinople.