E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Sacco Benedetto or Saco Bendito [the blessed sack or cloak].
A yellow garment with two crosses on it, and painted over with flames and devils. In this linen robe persons condemned by the Spanish Inquisition were arrayed when they went to the stake. The word sack was used for any loose upper garment hanging down the back from the shoulders; hence sac-friars or fratrs saccati.