In 1967, an organizer tried to remove Kathrine Switzer from the Boston Marathon because she was a woman: she kept running, finished the 42 kilometers wearing bib number 261, and five years later Boston opened its doors to women

Kathrine Switzer was 20 years old and had a number pinned to her back: 261.

On April 19, 1967, she registered for the Boston Marathon using her initials, K. V. Switzer, because the race was for men only and no one suspected a thing. People said that running more than 42 kilometers was harmful for a woman: too fragile, too weak. She had been training for months to prove that this was a lie.

At the halfway point, an organizer realized. According to Amnesty International, he tried to forcibly remove her from the race. Photographs of that moment went around the world and showed just how far resistance could go to women occupying spaces that had long been denied to them.

Kathrine didn’t stop. She finished the race.

In 1972, Boston finally opened registration to women. And in 2017, at 70, she ran the same marathon again with the same bib number, fifty years later.

How many doors will 261 have opened for the women who came after?