Cloak

The Roman Soldier’s Coat
When the weather turned cold, wet, or windy, a tunic wasn’t enough. A Roman soldier could wrap himself in a sagum, a plain military cloak worn over everything else.
It wasn’t the hooded cloak you see in pictures, just a large piece of woolen cloth, usually pinned at the shoulder with a brooch. That simple design made it surprisingly useful. A soldier could wrap it tight on a cold night, throw it back when he needed his arms free, or pile it on for warmth while resting.
It also read as military. A sagum could mark a man as a soldier even when he wasn’t in armor.
And unlike most military kit, its purpose hasn’t changed in 2,000 years:
When you’re cold, wrap yourself in a big wool blanket and keep going.