From the perspective of the origin of the word “cassock”, the name derived from early French, meaning a long fur lining coat which keeps people warm in the deep winter. It is also believed that the cassock is historically originated in ancient Rome by the sixth century. The clerics and nobility adhered to the conventional Roman style of costume with a long tunic and loose cloak that was worn beneath the toga, whereas the lay folk were constantly shifting to wear the short tunic, mantle, and breeches influenced by the Barbarians. The entire Western Christendom has been impacted more or less by the styling trend from Roman.
The adoption of the original version of the cassock with the hemline reaching the feet represented the modesty. Since the fifth century, a number of synods made rules to prevent clerics from wearing richly styled attire, tightly fitting clothing or luxurious ornaments and accessories. The canons of the Council of Braga in Portugal (572) was the very first of the aforementioned synod to request the clergy to wear a long tunic. Even in far-flung Britain, the archaeological evidence reveals the absence of the short tunic both among the Celts and Anglo-Saxons when it comes to clerical service. In the meantime, synodal regulations on restraining the tendency of the clerics to wear the reinvented short cassock were rising continuously. The reports of laxity in England indicated that Pope John VIII (c. 875) foreworn the highest Bishop of Canterbury and York to make sure their clerics choose appropriate styles of the cassock, long Roman tunic in particular.
During the Medieval period, the dress code of the clerics was overseen by the law of the Christian church, with a small number of complementary decrees passed by local synods. The Fourth Lateran Council (1215) set the specific rules of permitted clerical garments in regards to the colors, silhouettes, front and back length, as well as every ornamental detail. In 1237, the national council noticed that the laity were ashamed at the wearing of the clergy, which was not perceived as the clerical dress at all but was more suitable for knights. The subsequent regulations promulgated by the church were more rigorous. Violators in the future were supposed to be punished. Hence, the appropriate wear of the medieval clergy was vestis talaris (a sort of earlier cassock, similar to a long tunic with a button-fixed closed-opening front.)
Until the early modern era, the legislation regarding the clergy attire become more relaxed. The clerics were permitted to wear a short cassock if they were on travel or on vacations. Nonetheless, the color of the cassock should be black still and the bottom ought to at least reach the knees so as to differ from the lay apparel. Nowadays, constraints of the regulation are much lighter. Although, wearing the classic cassock is still the mainstream for most of the priests in terms of the distribution of Holy Communion around the parish and a normal suit with a tab-collar or a clergy shirt is widely accepted in priests’ daily duty.