SELMA, Ala. (AP) — People are remembering the bloody clashes that took place between police and demonstrators 50 years ago during the civil rights struggle.

Police estimated at least 15,000 to 20,000 people crowded on and around an infamous bridge in Selma, Alabama, on Sunday to remember the 1965 voting rights march that turned into "Bloody Sunday" when police beat and tear-gassed marchers at the foot of the Edmund Pettus Bridge.

The attack on March 7, 1965 helped build momentum for passage of the Voting Rights Act later that year.

Many of this Sunday's marchers held up signs and some chanted or sang hymns.

One sign raised in the crowd, read "Black lives matter, all lives matter."

On Saturday, civil rights leaders and President Barack Obama and his family participated in the weekend's commemorative events. Former President George W. Bush was also there.

An anniversary march from Selma to Montgomery is set to begin Monday morning and culminate with a rally at the Alabama Capitol on Friday afternoon.