ROTUNDA, a term applied to buildings which are circular in their plan both externally and internally, or else to halls and other apart ments of that shape, included within and forming merely a portion of the edifice containing them. The technical application of the term is however restricted to circular buildings whose height does not much exceed their diameter, for wo should not describe a lofty cylindrical edifice, such as a round tower, by the term rotunda ; white on the contrary it is frequently employed to designate polygonal buildings which approach in their general form to the circle.
In ecclesiastical architecture circular and polygonal structures were by no means uncommon among the early Christians, especially for baptisteries and sepulchral chapels. The tomb of Theodoric, or what is now called Santa Maria Rotunda, at Ravenna, is a singular example, having a flattish or segmental dome (about 34 feet in diameter) cut out of a single block of atone. Of San Stefano Rotundo and Santa Coetanza mention has been made under Romax ARCIIITECTIME, and to them may be hero added the Rotunda or Church of Santa Maria Maggiore at Nocera, a work of about the same period. While it greatly resembles Santa Costanza in plan, having coupled columns placed on the radiating lines from the centre, and with arches springing from them, it differs altogether hi section from both those examples, there being no cylindrical wall or tambour above the colonnade, but the dome springs immediately from the columns, and the arches mining into it. Consequently the proportions are much lower, the diameter of the space enclosed by the columns being 39 feet, and the height to the top of the demo 42,—proportions differing rely little from those of the Pantheon. The extreme internal diameter is 78 feet. The earlier edifices of this class are, for the most part, of moderate dimensions, but others were afterwards erected on a larger scale, and among them is the celebrated baptistery at Pisa Plarrisreav], which is externally about 120 feet in diameter, and 100 in height, exclusive of the dome. Circular churches, or baptisteries, arc also of frequent occurrence in Germany and Franco; and in England arc three or four round churches of semi-Norman (12th ceutury) character which are supposed to have been designed in imitation of the Church of tho Holy Sepulchre at Jerusalem : such are the round churches at Ounbridge and Northampton, and the Temple Church, Loudon.
The rotunda became afterwards in a manner incorpomted with or added to the cruciform plan, being raised aloft and placed over that part of it where the transepts intersect the body of the edifice. Nearly all modern cupolas may be described as rotundas elevated above the rest of the building and viewed by looking up into them from below. Thus suppoaing there was a floor at the level of the whispering gallery at St. Paula, the dome aud space beneath it would form a perfect and well proportioned rotunda, whose height aud diameter would very nearly be the same.
In itself alone the rotunda form does not accommodate itself to the purposes of a church : it does not afford space for the processions and occasional ceremonies required by the Roman Catholic worehip ; nor is It better fitted for the Protestant service from its requiring an amphitheatrical arrangement of seats iu concentric curves. Rotundas are accordingly rare even in Roman Catholic churches, yet although such structures are necessarily limited by their form to a moderate size, they derive from It also a grandeur which would not be produced by the same scale according to any other plan. Neither grandeur nor beauty however results as matter of course from the plan alone, because whatever charm that possesses may be nullified by other circumstances. There is, for instance, nothing of the one and not very much more of the other in the rotunda interior of St. I'eter•le I'oor's, London, one of the few instances we are acquainted with of such plan being adopted for a Protestant Church. The arrangement of the pews and seats in parallel rows, strikes as a disagreeable con tradiction to the shape of the building ; and in this case the 'vaulted dome, which is almost essential to such plan, is wanting, a cove and lantern with windows being substituted for it. Some few dissenting chapels have been built of a circular form, but they are equally unsatisfactory, whether regarded as architectural objects, or for con gregational purposes.