This unusual garment is called a “Bishop’s Mantle,” because of its similarity to the robes worn by such clergymen, but if you look closely, you’ll see it’s made up of linked chains — and is actually armor.
In fact, it probably was only dubbed a “Bishop’s Mantle” by 19th-century antiquarians, and we might think of it more properly as a cape of mail. The cape was designed to go over the shoulders and upper torso down to where it met the elbows, and was worn by infantrymen. This one is from the 16th century in the area where modern Germany is now.
Chain mail was the most effective kind of armor in Europe, starting from the third century BCE to the early fourteenth century CE. By the time this particular cape of mail was put together, however, plate mail had superceded it — chain still continued, particularly as a way to protect vulnerable areas of the body between the plates.
Metal armor was very heavy — this piece was incredibly lightweight at only 9lbs, 1oz — something that soldiers on foot could actually put up with.
Sources: Information from the NYC Metropolitan Museum of Art, @metmuseum.org. Armor and specifics from the St Louis Art Museum
