DEAMBULATORY. - By d., or peribolos or ambulatory, is generally meant an annular corridor that runs around the apse, often continuing the side aisles.
In buildings with a central plan the d. is found between the perimeter wall and the central space. The church of the Holy Sepulchre in Jerusalem was imitated in circular constructions provided with a d. that runs around the entire perimeter wall of the building. Similarly, in the mausoleum of Constantina, or church of St. Constance in Rome, the d. runs between the outer walls and the twelve pairs of columns that support the arches on which the high drum of the dome rests; the Lateran baptistery too presented a dome and a vaulted d., with a disposition similar to that of St. Constance. To this same type are linked, in Rome, the church of St. Stephen Rotondo and, in Perugia, that of St. Angelo.
As a curvilinear corridor that runs around the apse, the d. already existed in the most ancient basilicas, as at Porto and at Parenzo in the remains of the primitive church, in the remains of the urban basilica of Salona, probably of the 4th century, bounded by a semicircular parapet that ran around the apse; in Rome, in the primitive basilica of St. Mary Major, in St. John Lateran, in St. Lawrence outside the Walls, and in St. Severus in Naples, the d. resulted from the very structure of the apse opened with columns and arcades. Likewise at Nola in the basilica of St. Felix, and in the church of St. John Major and of St. George Major in Naples. Later a d. is found in the apse opened by arcades of the small basilica of Prata near Avellino, perhaps of the 7th century. In some constructions later than the 8th century the ambulatory develops so much as to appear as the continuation of the side aisles; in the Carolingian age, in St. Martin of Tours there was a d. with radial chapels, that is, opening onto the d. itself. Perhaps of the 10th century is the apse of St. Stephen in Verona, with an ambulatory with two superimposed galleries. A broad d. is found in the cathedral of Ivrea, built between 969 and 1002. Much later must be considered the peribolos of St. Sophia in Padua, where the apse is internally opened by niches.
In the Romanesque period this architectural motif was used in Italy only sporadically, while in France it took on complex forms, especially with the opening of radiating chapels onto the d. These chapels, in Italy, are found in the church of the Benedictine abbey of St. Antimo in Tuscany, under foreign influences, and again only in St. Mary at Pié di Chienti (Marche), at the Holy Trinity of Venosa, in the cathedral of Acerenza and in the cathedral of Aversa, where however the d. presents ribbed vaults, different therefore from those of d.'s covered by groin vaults.
In France the d. is found in a great number of Romanesque churches. However, it is found only rarely in the Provençal, Germanic and Norman schools. For the most part the apsidal chapels open onto the d., but there are also d.'s without chapels and chapels that open directly onto the apse, without the d. (this disposition could be traced back to Roman constructions, such as the Pantheon and the Nymphaeum of the Licinian villa). In the Gothic period the d., always highly developed outside Italy, appears frequently among us too; it is found in the Franciscan church of St. Lawrence Major in Naples, built under French influences, and in St. Francis of Bologna, which has around the apse a peribolos with nine radial chapels. An apsidal peribolos with radiating chapels is also in St. Anthony of Padua; an apse with d. is also presented by the cathedral of Milan.
In churches provided with an ambulatory and radiating apses, the choir achieves a great effect, which on the outside becomes even greater because of the way in which the various parts that compose it come to be arranged, and because of the elegance of the decoration, richer than in the interior. Thus in the churches of Notre-Dame-du-Port at Clermont Ferrand, in the church of Orcival, in St. Saturninus of Toulouse, etc.
After the Gothic period the d. disappears together with the other peculiarities of Romanesque and Gothic buildings. In Rome in the 17th century a d. is found quite exceptionally in the Lombard national church of the Sts. Ambrose and Charles at the Corso, perhaps due to a recollection of the cathedral of Milan.
