The Ambulatory As Circulation Around The Sanctuary

An ambulatory is a covered walkway that curves around the apse behind the high altar, continuing the side aisles of the nave in an unbroken path that lets worshippers, and especially pilgrims, circulate fully around the sanctuary without ever crossing through the space reserved for the altar and clergy. Structurally the ambulatory is simply an extension of the nave's side aisle system, bent to follow the curve of the apse rather than terminating flatly at the church's east wall, and it is frequently ringed on its outer edge by a series of small radiating chapels, sometimes called a chevet when the apse, ambulatory and chapels are considered together as a single integrated composition.

Practically, the ambulatory solves a real logistical problem in any large church that expects significant pilgrim traffic: it lets a continuous stream of visitors move past relics, side altars or venerated images housed in the radiating chapels, and past the main sanctuary itself, without disrupting the liturgy taking place at the high altar or requiring pilgrims to double back along the same route they entered by. Not every church has an ambulatory; simpler parish churches with a flat or shallow apse and no expectation of pilgrim traffic typically dispense with it entirely, making its presence a reasonably reliable indicator that a given church was built, at least in part, to accommodate large-scale pilgrimage.