Sack-back gown

This style of gown had fabric at the back arranged in box pleats which fell loose from the shoulder to the floor with a slight train.

Scalloped ruffles often trimmed elbow-length sleeves, which were worn with separate frills called engageantes.

The casaquin (popularly known from the 1740s onwards as a pet-en-l'air) was an abbreviated version of the robe à la française worn as a jacket for informal wear with a matching or contrasting petticoat.

[5] A popular story, traced back to the correspondence of Élisabeth Charlotte d'Orléans, Duchess d'Orléans, is that the earliest form of the sack-back gown, the robe battante, was invented as maternity clothing in the 1670s by Louis XIV's mistress to conceal her clandestine pregnancies.

"[6] A similar story is associated with Marie Louise Élisabeth d'Orléans, Duchess of Berry, who during the French Regency of 1715-1723 was known for wearing this style of gown which showcased her bosom and face whilst, as with Madame de Montespan, disguising illicit pregnancies.