BALAÚSTRA. – A railing composed of vertical elements identical to one another, called balusters or small balusters, often rising from a common base and always joined at the top by a flat element serving as a sill; this plane may correspond to the possible lower member. It is clearly distinct from the transenna, since the latter, instead of being formed, like the balustrade, of independent and repeated elements, is a perforated pluteus. The balustrade in its most common form originated in the system of enclosing loggias when, through the application of the Gothic principle of eliminating inert masses, solid parapets or plutei were articulated into individual vertical supports. In religious architecture its precise purpose is to enclose or separate certain areas from the rest of the church and it therefore replaces plutei, parapets, and transennae; it consequently became necessary when, after the abolition of the raised presbyteral area characteristic of the Romanesque period, the pluteus or transenna had also fallen out of use. It was likewise regularly used to restrict access to chapels when, in the fifteenth century, the luspaterrato developed and hence the desire arose to isolate the tombs or the family area from the common space of the naves. The form of the balusters and the colour of the marbles varied considerably over time. On the whole, the balustrades of sacred buildings followed the development of those of civil constructions. In the fifteenth century there are still a few rare examples of transennae, such as those with amphorae among scrolls in the old sacristy of S. Lorenzo in Florence; but already in the pulpit of S. Maria Novella the balustrade has differentiated vertical elements in the form of little columns. In examples by Michelozzo or in the Carafa chapel in S. Maria sopra Minerva in Rome, the baluster has become elegantly slender at the ends, differentiating into two symmetrical halves. A few solid railings still survive, also called, although improperly, balustrades, such as the Roman one in S. Maria del Popolo from the workshop of A. Bregno.
Already at the beginning of the sixteenth century, the elegant and slender line of the balusters yielded to greater massiveness, which weighed down the curves, while the recesses became more pronounced; finally, of the two similar halves only the upper one remained, and the other was replaced by a small base. This evolution took place rapidly in Rome, from Bramante to Sangallo and Vignola; Giacomo della Porta was already accentuating the swellings and recesses in the church of S. Maria dei Monti. With Maderno, the balustrade came to be used as the terminal element of a façade along the two slopes of the pediment (S. Susanna), so that the plastic masses might expand into space through a more gradual transition. In the cloister of S. Carlino alle Quattro Fontane, Borromini set a straight baluster beside an inverted one in order to create, even in a part necessarily devoid of movement, a continuous and insistent rhythm. Meanwhile, during the seventeenth century, the colours of the marbles became more vivid, the curves were increasingly accentuated, and the balustrade as a whole lost its original straight course. Pietro da Cortona, in the Gavotti chapel in the church of S. Niccolò da Tolentino, used balusters of complex profiles and square sections; finally, Borromini, in the Spada chapel in the church of S. Girolamo della Carità, with imaginative adherence to the function of the balustrade during the administration of the Eucharist, eliminated every architectural element and replaced it with a marble drapery supported by angels. In the eighteenth century, the tones of the marbles became subdued, the profiles lost their seventeenth-century softness, and the sense of emptiness once again predominated. Nineteenth-century architects drew variously upon forms of the past according to the orientation of their eclecticism. In modern constructions, on the other hand, when the motif of the transenna is not revived, the individual vertical elements are reduced to their essential function as supports with square or circular sections, and the architect’s interest is directed chiefly toward proportions and spacing.