There are many time periods, and many ways of measuring them. The Jurassic. The Victorian. The Dot-Com. But there is one period that goes across all periods, and that is the menstrual period. Menstruation is as old as humankind! And yet, it is so often left out of the history books. This erasure is rooted in a cultural legacy treating bleeding as if it’s something to be ashamed of. Advertising menstrual products on television was banned until 1972, despite more than half the population purchasing and using them around once every 28 days. If that ban hadn’t been lifted, we never would have had Courteney Cox’s glorious 1985 Tampax commercial, above.

It’s time to rewrite history. Welcome to a period-positive space, and a new look at time, through a lens of menstruation. Grab your BFF and peruse this slideshow that’s dripping with information. From the invention of the beltless pad to the free-bleeding run of a marathon, we put together a few moments in menstrual history that will make you proud to be a member of the club.