Four centred arch

A four centred arch is low, wide and pointed: each side turns on two centres, a small one on the springing line and a large one far below it. John Henry Parker dates the Perpendicular style from 1377 to 1547. In its later windows, he writes, the four centred arch “began now to be extensively used” and “was gradually depressed, until all beauty of proportion was lost”. Its doorways “have generally one prevailing form, which is a depressed arch within a square frame, and over this a label”; the west doorway of Fotheringhay, of 1435, has “foliated circles in the spandrels”. Parker gives no way of drawing the arch, so the construction here is our own, and it is exact. The span is quartered by vesicas, as for the ogee arch. About each quarter point, at half the span, the upright is cut below the springing, so the four points make a square under the arch. A line from each lower corner through the quarter point on the other side runs on to cut the small circle about that point, swung at a quarter of the span from the springing. About the lower corner, through that crossing, the large circle runs to the middle and meets its pair. The two circles have their centres on one line through the crossing, so the curve turns there without a break. The crown stands 0.4239 of the span above the springing. The square frame, the label and the foliated circles follow Parker’s doorway; they are drawn from the arch’s measures, each circle as large as its spandrel allows.