Order the church as a single path: a colonnaded atrium, a narthex, the long nave drawn toward the altar, and the apse framed by a triumphal arch at the end of the axis.
The chevet: ambulatory and radiating chapels
End the choir in a semicircle of piers; wrap an aisle (the ambulatory) around it, and open a ring of chapels off the ambulatory, each with its own altar and windows, so that the east end steps down in tiers of roofs and buttresses.
The ambulatory with radiating chapels was a Romanesque invention of the pilgrimage roads; Suger’s Saint-Denis made it Gothic by merging chapels and ambulatory into a single space under rib vaults, with windows all round. In the great cathedrals the chevet became the most complex part of the building, where the piers of the hemicycle, the trapezoidal ambulatory bays and the flyers radiating from each pier all had to be set out from one centre.
Related rules
To make a square of half the area of another, join the mid-points of its sides: the rotated square so drawn has exactly half the area. Repeat to halve again.
side of inscribed square = s ⁄ √2 · area = ½ s²
Put the hall at the heart of the house and enter it at one end, by a passage running through the house from front door to back door, screened from the hall. Open the buttery, the pantry and, between them, the way to the kitchen off that passage, at the hall’s lower end; put the family’s parlour, and the great chamber over it, beyond the hall’s upper end, where the high table stands.
Lay out the church as an Early Christian basilica (a tall nave lit from above, lower aisles on either side, a sanctuary ending in an apse to the east) and cross it with a transept, so that the plan becomes a Latin cross with a tower over the crossing.
Let the square of the crossing set the measure of the whole church: the nave and transept arms are multiples of it, each nave bay is a square of the same size, and each aisle bay a square one quarter its area.
nave bay = crossing square; aisle bay = ¼ of it; nave length = n squares
Multiply altars at the east end by opening apses off the transept arms and the choir, stepped back from the main apse in echelon, each with its own small semidome and roof.
Cite this page Chris Paton, “The chevet: ambulatory and radiating chapels”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/gothic-chevet. Text, drawings and models licensed under CC BY-NC 4.0.