The sagum is a very simple garment worn by members of the CCR; all members of the CCR who are milites or equites are entitled to wear it.
Whereas for the Romans it was a garment of violent war, for the CCR it is a garment of spiritual war, of our dedication to be soldiers of Christ and to fight for the establishment of the reign of Christ the King.
The sagum is, originally, an old Roman garment, principally worn by soldiers. The Romans regarded the toga as a garment of peace, while the sagum was a garment of war.1 It consists essentially of a large rectangle of (usually woolen) cloth, which was wrapped around the shoulders and fastened over top of the armor. Typically, it was fastened not in the center, but to one side, and it would be dyed bright red to signify its martial meaning.
This simple garment, of course, has always been quite common, and by no means was it unique to the Romans. Charlemagne famously wore a form of the sagum, but his was colored blue (sago veneto; 2), an important distinction for the form of the CCR's sagum. We don't necessarily know how long it was, but Notker notes that:
The last part of their dress was a white or blue cloak in the shape of a double square; so that when it was placed upon the shoulders it touched the feet in front and behind, but at the side hardly came down to the knees.3
Charlemagne is noted to have been very disapproving of a
developing custom, toward the end of his reign, of wearing
shorter, less full cloaks, referring to them scornfully as
little napkins
(pittaciola).4
The CCR sagum is of the same form as Charlemagne's: a large double-square, or near it, one of the short ends of which is fastened over the shoulder. The Simple Arms is placed on the left side of it, and it is fastened over the right shoulder, so that the arms will lie over the wearer's heart (or near it). This is also opposite the martial garment's habit: traditionally, it was fastened over the left shoulder, so that it would not interfere with drawing the sword which hung from the left hip.
So the CCR sagum is summed up as follows:
We wear the sagum at meetings, when we are in processions, and when engaged in any public ceremony. The sagum is an honor to wear, and its dignity should be scrupulously protected.
Christus vincit! Christus regnat! Christus imperat!