Around the central space, beyond the row of columns, an area is designed to allow the faithful to walk around. This area is called the ambulatory.
Notre-Dame de Paris is characterized by a double row of columns forming the aisles. During an enlargement of the building in the 13th century,
chapels were placed around the aisles. These double aisles and the double ambulatory of the choir are a unique example in medieval religious architecture.

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