ARCADE, a range of apertures with arched heads, sup ported upon square pillars, or other columns. Arcades are sometimes employed to form porticos instead of colonnades ; and though they are not so beautiful, they arc stronger, more solid, and less expensive. In such buildings, the utmost care should be taken that the piers be sufficiently strong to resist the pressure of the arches, particularly the piers at the extremities, for they alone support the whole.
The lateral pressure upon the extreme piers in the range, will be equal to that on the piers of a single arch, and all the intermediate piers will be without such lateral pressure ; for the lateral pressures of any two adjoining arches upon the intermediate piers are equal, and being opposite they destroy each other's effect : but the extreme pier having only one adjoining arch, must be sufficiently strong to withstand the horizontal thrust of that arch. The greater the weight or vertical pressure put upon the extreme piers, the more will these piers be able to counteract the thrust of the adjoining arch ; consequently, if each extreme pier have to support a wall, the higher the wall, the less dimensions the pier requires. It is upon this principle, that the slender pillars dividing the nave on either side from the aisle, in churches? of the Saxon and pointed styles of architecture, are capable of withstanding the horizontal thrust of the groins ; for if the insisting wall were taken away, the pillars of most of these buildings would not be able to withstand the thrust of the arches for one minute.
Arcades were employed in triumphal arches, theatres, amphitheatres, and aqueducts of the Romans, and frequently in their temples : towards the decline of the empire, the intereolumns were formed into arcades ; but what relates to their history will be found under the article ARCH.
Arcades may be used with propriety in the gates of cities, palaces, gardens, and parks: they are much employed in the piazzas or squares of Italian cities, and, in general, are of great use in both shade and shelter in hot and rainy climates ; but they are nevertheless a great nuisance to the inhabitants, as they very much darken their apartments.
Lofty arcades may be employed, with great propriety, in the courts of palaces and noblemen's houses. There arc various methods of decorating the piers of arcades, as with rustics, columns, pilasters, caryatides, persians, or terms surmounted with appropriate entablatures. Sometimes the piers are so broad as to admit of niches between columns or pilasters. The arch is either surrounded with rustic work, or with an archivolt, sometimes interrupted at the summit by a key-stone in the form of console, or mask, or some other appropriate ornament in sculpture_ The archivolt rises sometimes from a plat-band, or impost, placed on the top of the piers, and at others from an entablature, supported by columns on each side of the arch. In some instances, the arches of arcades are supported entirely by single or coupled columns, without the entablature, as in the temple of Faunus, at Rome. This form is far from being agreeable to the eye, and it wants stability, as the columns would be incapable of resisting the lateral pressure of the arches, were they not tied together by a circular wall. In large arches, the key
stone should never be omitted, and should be carried to the soffit of the architrave, where it will be useful for supporting the middle of the entablature, which would otherwise have too great a bearing.
When columns are detached, as in the triumphal arches at Rome, it is necessary to break the entablature, and make its projection in the intere.olumns the same as if pilasters had been used instead of columns, or so much as is just suf ficient to relieve it from the naked appearance of the wall ; this is unavoidable in all intereolumns of great width; but should be practised as little as possible, as it destroys the genuine use of the entablature. Arcades should never be much more, nor much less, than double their breadth : the breadth of the pier should seldom exceed two-thirds, nor be less than one-third of that of the arcade ; and the angular pier should have an addition of a third or a half; as the nature of the design may require. The impost should not be more than one-seventh, nor less than a ninth ; and the archi volt not more than one-eighth, nor less than a tenth of the breadth of the arch. The breadth of the bottom of the key stone should he equal to that of the archivolt, and its length not less than one and a half of its bottom breadth, nor more than double. In porticos, the thickness of the piers depends on the width of the portico and the superincumbent building ; but with respect to the beauty of the edifice, it should not be less than one-quarter, nor more than a third of the breadth of the arcade. When the arcades form blank recesses, the backs of which are pierced with doors, windows, or niches, the recesses should be at least so deep as to keep the most prominent part of the dressings entirely within their sur face.
In the upper stories of the theatres and amphitheatres of the Romans, the arcades stood upon the podiums or inter pedestals of the columns, perhaps as much for the purpose of proportioning the apertures, as to form a proper parapet for leaning over.
In Gothic -Architecture—arcades, whether detached or engaged, are of very frequent occurrence; more especially in the Transition and early English styles. Engaged arcades are very common indeed, and may be found frequently running round the interior walls of a building, as at West minster Abbey, the Chapter-House, Canterbury, and ininnumerable other instances; in the conventual buildings at Canterbury is a very fine specimen of a detached arcade. The. engaged form came into very extensive use with the intersection of the semicircular arch, and was employed in almost every situation both on the interior and exterior of buildings, as well as in the decoration of their furniture, such as fonts, &c. The arcade indeed was a very prominent., if not the principal feature in all Gothic architecture, and is that which adds so greatly to the solemn grandeur of our noble cathedrals.
This term is also applied to any arched covered way, more particularly to the close passages recently introduced, such as the Burlington and Lowther arcades, which are used as promenades, as well as for purposes of trade.