History of Scapulars (https://en.wikipedia.org/wiki/Scapular)
The scapular may have emerged from an apron-like piece of cloth worn by monks. Item 55 of the Rule of Saint Benedict, dating to the 7th century refers to the use of the scapular.
In the Western Church the key elements of a monk's habit eventually became the tunic, the cincture, the scapular and the hood. A nun's costume included the tunic, the scapular and the head veil.