The first female Freemason was initiated by surprise

Elisabeth Aldworth was the first woman initiated into speculative Freemasonry in Ireland around 1712. She inadvertently discovered the rituals of a secret lodge that was meeting in her father's house. The members then decided to integrate her officially to ensure her silence. Following this event and the creation of the first Grand Lodge in England, the ban on admitting women was formally institutionalized for more than a century.