The excavated ancient Villa Romana del Casale in Southern Italy is known for two things: the largest and most intricate set of Roman-Empire mosaics, and for those mosaics depicting women participating in athletic events seemingly dressed in very modern bikinis. Whether Louis Réard was inspired by them or something more out of his own imagination is unclear, but his two-piece swimsuit, consisting of a top made of two swatches of fabric connected by a string, and a bottom that for the first time exposed the navel, was the first bikini.

On this day, July 5, in 1946 Réard introduced his bikini, the world’s smallest bathing suit. Réard’s competitor Jacques Heim had introduced previously “the smallest bathing suit” of his own, called the Atome, which Réard shrunk even further, saying he had “split the Atome.” In a pique of wordplay, he chose to name his new line of clothing after an atoll in the South Pacific where the U.S. tested atomic bombs.

Réard’s bikini became a big hit, particularly among men, who sent to him 50,000 fan letters. Réard did what he could to trump up his business, hiring a former exotic dancer to model his invention, and declaring in advertisements that no two-piece was a genuine bikini “unless it could be pulled through a wedding ring.”