How did the justaucorps help inspire the modern three-piece suit?

The justaucorps—a knee-length, fitted coat—was a foundational element in the evolution of the modern suit. During the 1660s, at the courts of Louis XIV and Charles II, men’s fashion shifted toward a style consisting of this long coat worn over a vest (later known as a waistcoat) and breeches.1

This ensemble established the concept of a coordinated set of garments, which is the direct ancestor of the modern three-piece suit. Initially, the vest was an undergarment nearly identical to the coat, often featuring long sleeves that extended past the coat's cuffs before eventually becoming sleeveless. While the original 17th-century style lacked collars and lapels, it introduced the standardized layering of a coat, vest, and lower-body garment that defines the three-piece suit today. Over the following centuries, this silhouette evolved through the 19th-century "lounge suit" into the contemporary professional attire recognized today.12