This week's WTA Championships in Istanbul mark the culmination of the 40-year anniversary of two of the most significant events in the history of tennis.
Nowadays tennis is the most prominent and lucrative of women's sports, a situation made possible in no small part by the formation of the Women's Tennis Association in 1973, the same year which saw Billie Jean King take on and defeat Bobby Riggs in the 'Battle of the Sexes'.
Throughout this season the WTA has been celebrating the landmarks, with good reason given the remarkable progress that has been made in the intervening decades.
The story began in 1970 when nine female players, known as the Original Nine, set up the Virginia Slims Circuit as a protest against the vastly unequal amounts of prize money which were being awarded in the new Open Era of tennis.
Prize money for men would often be five times greater or more than that of women. At the first Wimbledon of the Open Era King won £750, this year Marion Bartoli took home £1.6 million.
Despite opposition from the United States Lawn Tennis Association, the tour's members had swelled by the end of the year and a full calendar of events was put on in 1971.
The Circuit would go from strength to strength and in 1973, King gathered 63 players together at the Gloucester Hotel in London just before Wimbledon for a meeting which would ultimately result in the formation of the WTA.
Earlier that year the 55-year-old Riggs, a former world No 1 in the men's game, had beaten Margaret Court comfortably in an inter-gender clash. Another challenge was set up in August, with Riggs this time going up against King.
King won a much-hyped, highly-publicised best-of-five set match 6-4 6-3 6-3. The event was celebrated this summer with a film.
The exposure of the women's game has been increasing ever since and six years ago a major milestone was achieved, when all four grand slams paid the same prize money to men and women for the first time.
Over the last three years $200 million has been ploughed into the women's game, which stages 54 tournaments in 33 countries, but WTA chief executive Stacey Allaster has recently been keen to take the time to highlight those ground-breaking events 40 years ago.
"I'm in tennis, and I thought I knew the story," Allaster said in her State of the WTA address in Istanbul.
"But I must tell you this year has been such an educational year for me personally to learn more about how hard it was to be a woman in 1973, how hard it was for Billie, and the weight of the world that she had on her shoulders and the significance of what a tennis match was where it did change the lives of women forever.
"Serena (Williams) talked about Billie giving her and all the players an opportunity to play tennis. I truly believe, had it not been for the Original Nine, had it not been for Billie beating Bobby Riggs, had it not been for the 40 years of the WTA, there wouldn't be a chance for a Stacey Allaster, a female, to be a CEO of a world governing body.
"I just couldn't be more proud and more confident in the product that we have to excel women's tennis for this next decade."