BALUSTRADE. - A railing consisting of vertical elements identical to one another, called balusters or little balusters, often rising from a common base and always joined at the top by a flat element serving as a sill; this flat element may be analogous to the possible lower member. It is clearly distinct from the chancel screen, since the latter, instead of being formed, like the balustrade, of independent and repeated elements, is a pierced pluteus. The balustrade in its most common form originated from the system of enclosing loggias when, in application of the Gothic principle of eliminating inert masses, solid parapets or plutei were articulated into individual vertical supports. In religious architecture it has the precise purpose of enclosing or separating determined zones from the rest of the church and therefore replaces plutei, parapets and chancel screens; it thus became necessary when, with the abolition of the raised presbyterial zone proper to the Romanesque period, the pluteus or chancel screen had also fallen into disuse. It was also used as a rule to limit access to chapels, when in the 15th century the floor tomb developed and with it the desire to isolate the burial or the family zone from the common space of the naves. The form of the little balusters and the color of the marbles vary considerably over the course of time. On the whole the balustrades of sacred buildings follow the development of those of civil constructions. In the 15th century there is still some rare example of a chancel screen, such as those with amphorae among scrollwork in the old sacristy of S. Lorenzo in Florence; but already in the pulpit of S. Maria Novella the balustrade has its vertical elements differentiated in the form of small columns. In Michelozzian examples or in the Carafa chapel in S. Maria sopra Minerva in Rome the little baluster is elegantly tapered at the ends, differentiating itself into two symmetrical halves. There still survives some solid enclosure also called, but improperly, a balustrade, such as the Roman one of S. Maria del Popolo from the workshop of A. Bregno.
Already at the beginning of the 16th century the elegant and slender line of the little balusters yields to a greater massiveness that weighs down the curves, while the hollows become more pronounced; finally of the two similar halves only the upper one remains and the other is replaced by a small base. This evolution is accomplished rapidly in Rome from Bramante to Sangallo and to Vignola; Giacomo della Porta already accentuates the swellings and hollows in the church of S. Maria dei Monti. With Maderno the balustrade comes to be used as a terminal element of a façade on the two slopes of the pediment (S. Susanna) so that the plastic masses expand with a more gradual transition into space. Borromini in the cloister of S. Carlino alle Quattro Fontane places an upright little baluster next to an inverted one to create, even in a part necessarily devoid of movement, a continuous and insistent rhythm. Meanwhile in the course of the 17th century the colorations of the marbles become more vivid, the curves are accentuated more and more and the entire balustrade loses its original rectilinear course. Pietro da Cortona in the Gavotti chapel in the church of S. Niccolò da Tolentino uses little balusters of complex profiles and square section; finally Borromini, in the Spada chapel in the church of S. Girolamo della Carità, with fanciful adherence to the function of the balustrade during the administration of the Eucharist, suppresses every architectural element and replaces it with a marble drapery supported by angels. In the 18th century the tones of the marbles become calm, the profiles lose their 17th-century softness and the sense of void returns to predominate. The architects of the 19th century drew inspiration in various ways from the forms of the past according to the orientation of their eclecticism. In modern constructions, on the other hand, when there is no return to the motif of the chancel screen, the individual vertical elements are reduced to their essence as supports of square or circular section and the architect's interest is oriented predominantly toward proportions and spacing.