Drum

DRUM. - A wall structure connecting the pendentives and the dome, cylindrical or prismatic in shape, generally, in the latter case, with an octagonal plan.

It is absent in the early Byzantine churches, since the dome is vaulted directly on the pendentives (Hagia Sophia, Sts. Sergius and Bacchus in Constantinople), and in the Romanesque centrally planned baptisteries given the tiburio-like conformation: the base structure — mostly octagonal — continues externally for the entire height of the dome, concealing its extrados, in order to form the support of the conical roof covering. Likewise, in the basilica of St. Mark in Venice and in that of St. Anthony in Padua, the drum is only apparent, but without a static function, because the outer dome serves only for protection, while the true masonry dome is set directly on the pendentives.

A first attempt, of undoubted classical inspiration, is observed in the cathedral of Pisa, where, however, the transition from the rectangular base zone to the oval dome is achieved by means of cuff-shaped pendentives rather than trumpet-shaped ones; later, in the cathedral of Siena, a dodecagonal structure analogous to the drum is found, inserted between the hexagonal plan of the crossing and the circular dome, but the iconographic irregularities determine constructive disorganization and a lack of compositional unity. Only at St. Mary of the Flower is a unified arrangement realized, though the octagonal plan begins from the load-bearing base structure itself, so that the connecting pendentives are eliminated and all the construction problems are simplified. The basilica of Loreto and the cathedral of Pavia are conceived on the same construction scheme. In other fifteenth-century churches of smaller dimensions, however, a further progress is made by setting the drum, always on an octagonal plan, above a square base by means of constructionally simplified connecting pendentives, given the junction with a flat wall (St. Mary of the People in Rome, St. Mary of the Graces or of the Calcinaio in Cortona, the cathedral of Turin, the Colleoni chapel in Bergamo). Externally these drums present smooth plastered walls or brick curtain walls, in which rectangular or round-arched large windows open; only at the beginning of the following century do the architectural orders appear, almost timidly, in St. Mary of Loreto in Rome.

But the fundamental innovation is introduced by Bramante, first in the tempietto of St. Peter in Montorio, abandoning the polygonal forms, a survival of the Gothic tradition, and setting the dome above a cylindrical body; and then, developing this classical conception, in the project for the Vatican Basilica where the architectural order becomes the dominant element in the architraved loggia, thus transforming the drum from solid into pierced. The Bramantesque conception, admirable for its clarity of proportions, has been rightly defined as a "magnificent illogicality" with regard to construction and statics.

The model for the following centuries, however, is found in the form given to the drum by Michelangelo, in which static requirements are ingeniously balanced with compositional unity, giving prominence to the load-bearing structure — pillars and columns in full projection — so as to concentrate the thrusts and to confer a sense of articulation and an expression of plastic power. The architects of the two following centuries adhered more or less faithfully to the Michelangelesque model, whether by repeating the motif of the colonnade (St. Andrew of the Valley and St. Charles at the Corso in Rome, the basilica of Superga, the new cathedral of Brescia, the cathedral of Catania), or by adopting pilasters in place of the columns (S. Maria di Provenzano in Siena, S. Carlo ai Catinari in Rome, the cathedral of Palermo, the cathedral of Como), while nevertheless preserving the broken entablature that imparts a sense of movement and a lively pictorial effect. The drum of S. Andrea delle Fratte in Rome stands apart from the others, since in its conformation, no longer cylindrical but on a mixed-line plan, it manifests Borrominian dynamism.

The stability of domes of considerable dimensions, especially if of low rise, sometimes determines interesting structural arrangements that also contribute aesthetically to making the connection between the different parts of the architectural organism more tightly knit: thus at S. Maria della Salute in Venice the drum is surrounded by the characteristic large volutes (the "orecchioni") that transmit the thrusts to the perimeter walls, while in the sanctuary of Vicoforte these are absorbed by enormous tower-like buttresses placed in correspondence with the ribs of the dome.

The nineteenth century coldly continues the preceding schemes, in the form of the loggia (S. Carlo in Milan) or in that, more responsive to neoclassical taste, of the completely closed cylindrical surface (S. Francesco di Paola in Naples). In the second half of the century historicist tendencies sometimes lead to the imitation of Renaissance forms (the cathedral of Cerignola, S. Maria Ausiliatrice in Turin); an entirely new conception is instead followed, with ingenious boldness, by Antonelli in S. Gaudenzio in Novara, dividing the drum into a series of superimposed loggias, of which the upper ones conceal the springing of the dome. - See plate CXXI.

Mario Zocca