Rules · Proportion · Optics · Plans
Proportion the width of an allée to its length: a walk of about 100 toises (some 200 m) should be 5 or 6 toises wide, one of 200 toises 7 or 8, and so on, so that a long walk does not seem to narrow to a slot in the distance.
100 toises long → 5–6 wide · 200 → 7–8 · 300 → 9–10 · 400 → 10–12 (1 toise ≈ 1.95 m)
A straight walk seen from one end narrows in perspective as it runs away. If it is too narrow for its length, the far end shrinks to a crack and the walk looks mean; if it is too wide, it loses the sense of enclosure that the palisades give it. Dézallier answers with a table: the width grows with the length, but more slowly. The main walk on the axis is the widest, often flanked by counter-allées (contre-allées) under the trees on either side, and the walks through the bosquets are narrower.
The widths are rounded here as they are in the book. They were applied with judgement: at Versailles the lawn of the Tapis Vert, with its side walks, is about 40 m wide for a length of about 330 m, wider than the table asks, because it is the king’s axis.
To find how thick the pier of an arch must be, divide the intrados into three equal parts; draw a line from the springing through the first division, and produce it beyond the springing by its own length. A vertical through the end of that line marks the outer face of the pier.
pier ≈ ¼ span (semicircle) · ≈ 0.23 span (equilateral) · less for a lancet
To unify a façade of two or more storeys, run a single order of pilasters or columns through all of them, from the base to the main cornice.
To combine the unity of a central plan with the direction a church needs, plan the space as an oval, set across the axis to widen the view of the altar, or along it to lead the eye towards it.
Divide the inside of a dome into coffers that shrink in step with the meridians as they rise, so that their perspective deepens the dome and draws the eye to the light of the lantern.
Let the wall of a façade curve in plan (concave, convex, concave) so that the front answers the street, the light and the space within, and the order bends with it.
Proportion every step so that twice its height plus its depth equals the length of a natural pace on the level: two feet, or 24 pouces.
2 r + g = 24 pouces ≈ 65 cm (modern practice: 60–66 cm)
Cite this page Chris Paton, “The allée widens with its length”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/dezallier-allee-width. Text, drawings and models licensed under CC BY-NC 4.0.