The long-awaited corruption trial of Istanbul Mayor Ekrem Imamoglu and more than 400 co-defendants has opened in a high-security court west of Istanbul, in a case widely viewed as a defining test of Turkey’s justice system and political future.

Imamoglu, the most prominent rival to President Recep Tayyip Erdogan, has been jailed for nearly a year. Despite his detention, he was chosen as the main opposition Republican People’s Party’s presidential candidate for the next national election, turning the courtroom into a focal point of Turkey’s power struggle.

The hearing began amid high tension. According to Turkish media, Imamoglu asked to address the court but was refused by the panel of judges, who then accused him of disrupting proceedings and briefly walked out, forcing an adjournment. Defense lawyers protested what they called an attempt to silence the defendant at the very outset of the trial.

The 402 defendants include senior officials and employees of the Istanbul Metropolitan Municipality, opposition mayors from district councils, and several journalists. Prosecutors allege that Imamoglu led a sprawling “criminal organization for profit” dating back to his tenure as mayor of the Beylikduzu district, using rigged tenders and kickbacks to enrich allies and bankroll his political ascent.

The indictment runs to nearly 4,000 pages and lists 142 separate charges. If found guilty on all counts, Imamoglu could face a cumulative sentence of more than 2,000 years in prison, as well as a lifetime ban from politics. He has dismissed the accusations as fabricated and described the proceedings as an attempt to “overturn the will of the people.”

His arrest triggered weeks of mass protests across Turkey, the largest street mobilization in years, with demonstrators accusing the government of weaponizing the courts to neutralize a popular opponent who twice defeated Erdogan’s party in Istanbul’s municipal elections.

Rights groups and legal experts have raised alarm over the use of anonymous “secret witnesses,” the pressure on some defendants to testify against others, and the role of Istanbul’s chief prosecutor, who previously served as deputy justice minister and has overseen a wave of cases targeting the CHP.

Authorities insist the judiciary is independent. Outside the Silivri prison complex, however, hundreds of supporters gathered in defiance of a protest ban, chanting for Imamoglu’s release as the trial that could reshape Turkey’s political landscape got under way.