The Catholic Encyclopedia
A cloister, gallery, or alley; a sheltered place, straight or circular, for exercise in walking; the aisle that makes the circuit of the apse of a church. The central eastern apse of a church was often encircled by a semicircular aisle, called the ambulatory. Of these ambulatories there are three species:chapels radiate to the north-east, east, and south-east. An ambulatory without radiating chapels is so rare in Romanesque work that supposed examples should be regarded as doubtful. Sometimes there is a rectangular ambulatory, as in the Romsey eastern chapel. Ambulatories are constructed either on the inside or outside of a building, or in a public thoroughfare wholly or partially under cover, or entirely open to the sky, and are used only to walk in. The term is sometimes applied to a covered way round a building, such as the space between the columns and cella of a peripteral temple, or around an open space as the cloisters of a monastic church, as the Campo Santo at Pisa, or the atrium of an ancient basilica, e.g. that of St. Ambrose at Milan. The term can be used as an equivalent of either cloister or atrium.
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Obstat, Nihil. Lafort, Remy, Censor. Entry for 'Ambulatory'. The Catholic Encyclopedia. https://www.studylight.org/encyclopedias/eng/tce/a/ambulatory.html. Robert Appleton Company. New York. 1914.