Thirty-six years before the original Rockettes appeared on a St. Louis stage in 1925,* a failed cotton magnate named John Tiller formed a dance troupe that featured quick, perfectly synchronized dance steps. By the 1920s, several dozen troupes of Tiller Girls, selected for uniform height and weight, performed in major cities across Europe. They were so popular that European revue directors formed similar troupes.
Lines of pretty women dancing, or at least posing, had been a staple of variety revues for years. The thing that made the Tiller Girls different from earlier chorus lines was their speed and precision, which many theater reviewers compared to the dynamism of the modern era. Tiller had created a human equivalent of the factory machine, with dancers as interchangeable parts in coordinated kick-lines.
*Yes. St. Louis. The Rockettes first hit Radio City Music Hall in 1932. I was surprised, too.