On July 1 that year, hundreds of protesters stormed Hong Kong's Legislative Council building after a protest march against a proposed extradition bill that would have allowed authorities to send individuals to mainland China for trial.
The protesters smashed glass and furniture, destroyed pictures and daubed walls with graffiti. While many of the protesters fled the scene without being arrested, local police later identified scores of them, including some of the 13 now on trial.
Rioting is punishable by up to 10 years in jail.
The seven who pleaded guilty included the former president of the University of Hong Kong's student union, Althea Suen, and pro-democracy activist Ventus Lau.
"I have never regretted fighting for freedom, justice, and democracy from the beginning to the end," Suen wrote in a Facebook post before the trial began.
"In 2023, I am in Hong Kong, in prison, but my mind remains free."
Six people pleaded not guilty, including actor Gregory Wong, and two reporters Wong Ka-ho and Ma Kai Chung. These six face additional charges of unlawful entry into the legislature and criminal damage which carries a maximum life sentence.
The trial is expected to last for 44 days.
"There is an end to all good and bad things," Wong told reporters outside the court. "No matter what the outcome, I think it's possible to be brave."
More than 10,200 protesters were arrested in connection to Hong Kong's anti-government, pro-democracy protests in 2019 over the since-withdrawn extradition bill, posing one of the biggest challenges to China's Communist Party leaders since Beijing's Tiananmen Square protests in 1989.
Around 2900 have been prosecuted on charges linked to the protests so far.
Following the protests, China imposed a national security law on Hong Kong that was criticised by some Western governments as a tool of repression with scores of democrats and activists arrested, while major civil society groups and liberal media outlets were shut down.
Hong Kong and Chinese authorities say the security law has brought stability to the global financial hub.
