BUENOS AIRES, Argentina (AP) — Thousands of Argentines took to the streets nationwide Monday to protest violence against women.

The marches coincided with the fourth anniversary of the founding of the activist group Ni Una Menos, or Not One Less. The Argentine grassroots movement has mobilized to fight gender-based violence and has spread to other countries.

"In these four years we've gained, and every time (the movement) is larger and more organized," said Verónica Gago, a movement activist. "You can see it in these marches ... and in the everyday organization at each workplace, in each university, in each school. It's in the debates among families and especially among the younger generations."

Ni Una Menos was created by 20 artists, journalists and activists in 2015 after outrage over a brutal string of murders. They began by organizing public readings about violence against women with family members of victims.

But when Chiara Paez, a 14-year-old pregnant girl, was killed by her boyfriend in May 2015, the organizers felt it was enough. The first call to protest started with a tweet by local radio journalist Marcela Ojeda: "Women: are we not going to raise our voices? THEY'RE KILLING US!"

The public outcry that followed on social media inspired the first march on June 3, 2015. That day, millions took to the streets of cities across Argentina, making headlines and triggering a nationwide conversation.

Argentina's Supreme Court reports there were 278 victims of gender-based violence last year.

Demonstrators on Monday marched from the Congress building to Argentina's historic Plaza de Mayo square, demanding an end to such killings and called on authorities to protect women. Many also carried signs in support of a bill recently introduced by lawmakers that would legalize elective abortion in Argentina.