Tens of thousands of Americans are gathering in Selma according to USA Today, Alabama this weekend to commemorate the 50th anniversary of an important moment in civil rights history.

Marchers are commemorating Bloody Sunday, a day when marchers tried to walk from Selma to Montgomery to demand an end to discriminatory polling practices. Police viciously attacked the marchers on March 7, 1965. The images were captured on television nationwide and served as a catalyst for civil rights.

An estimated 600 marchers headed to the Edmund Pettus Bridge on Bloody Sunday in 1965. John Lewis of the Student Nonviolent Coordinating Committee and the Reverend Hosea Williams led marchers to the bridge where they were met by a large group of state troopers blocking the other side of the bridge. Police officers and other white men beat marchers with nightsticks and fired tear gas into the crowd. Other troopers charged into the crowd on horseback. Roughly 17 people were hospitalized that day.

Afterwards, two more attempts were made to complete the 50-mile trip from Selma to Montgomery.

Due to the outcry from the violence captured on television, the Voting Rights Act of 1965 was ushered in in response to the marches.

President Lyndon B. Johnson's daughter, Luci Baines Johnson, traveled to Selma to join in the anniversary this week.

"This marks a sacred moment in our history," Johnson said. "There were so many heroes that led to this day, the ones whose names we know but also those who were fighting in the shadows and whose names weren't recorded in the history books."

Other participants began arriving Thursday for the five-day commemoration. President Barack Obama will speak at the foot of the bridge on Saturday. Other lawmakers and former president George W. Bush will also pay tribute to the fighters of the voting rights movement.

Despite the violence it took to achieve the Voting Rights Act of 1965, the Supreme Court struck it down two years ago. The court ruled that the Voting Rights Act formula used to determine which parts of the country would need federal approval to change voting procedures was outdated. In the ruling, the court instructed Congress to develop a new formula, reflective of current conditions, for new voting procedures. Congress has yet to develop a new rule.

Those who gathered in Selma this weekend congregated at some of the same churches used by civil rights leaders in 1965 to discuss voter ID rules and new voting laws that have been passed in some states.

"The voting rights act is being dismantled," said Kirsten Moller, who traveled to Selma from San Francisco to be part of the commemoration. "We need to protect it. It's not a given. We need to be vigilant."