The sack, or sacque, gown evolved from a very informal dress of the late seventeenth century into a formal dress by the mid-eighteenth century. The sack gown was first a loose, tent-like robe worn in the home or by pregnant women. The volume of the gown came from gathers near the shoulders and along the back. The front of the gown skirt was worn either open in the front to reveal a petticoat or stitched closed from the waist down to the hemline. As the century continued, these gowns became more formal, featuring fitted bodices, long full skirts, and a long box-pleated piece of fabric hanging from neck to ankles along their backs. These dresses were so often depicted in the paintings of French painter Antoine Watteau (1684–1721), the man who created the Rococo painting style that emphasized romantic love, that the pleats in back took his name: Watteau pleats. As the dresses became more fitted through the bodice, the gown came to be known as the robe à l'anglaise. The robe à l'anglaise was especially popular in England (anglaise means English in French) and featured a many-pieced bodice with a low neckline. The sack gown went out of style by the end of the century when Greek inspired dresses, such as the robe en chemise, became popular.
Bigelow, Marybelle S. Fashion in History: Apparel in the Western World. Minneapolis, MN: Burgess Publishing, 1970.
Laver, James. Costume and Fashion: A Concise History. 4th ed. London, England: Thames and Hudson, 2002.