From the base to the summit it is encircled, at regular distances, with broad bands of stone-work, disposed like scales; and, alternating with the bands, are perforations in the form of cinquefoils, quatrefoils, and trefoils, diminishing as the spire rises, but so disposed, that the light is seen distinctly through them.
"Account of a Tour in Normandy, Vol. II. (of 2)"
Dawson Turner
During the Middle Ages, when misdirected zeal credited almost any plant with healing virtues for every ill that flesh is heir to, the cinquefoils were considered most potent remedies, hence their generic name.
"Wild Flowers Worth Knowing"
Neltje Blanchan et al