A Tonneau case in watchmaking refers to a distinctive case shape that resembles a barrel or an elongated rectangle with curved sides. The term "tonneau" is French for "barrel," aptly describing the case's rounded, barrel-like silhouette. This design was first introduced by Louis Cartier in 1906, marking a departure from traditional round or square watch cases. The Tonneau case is known for its elegant and unconventional appearance, offering a unique aesthetic that contours to the wrist. It is favored by those seeking a non-traditional watch look, adding a touch of sophistication and individuality to the timepiece. The shape not only enhances the visual appeal but also provides a comfortable fit, making it a popular choice among watch enthusiasts who appreciate both style and functionality.