Following his defeat in the English Civil War, Charles I was tried by Parliament's revolutionary tribunal, an unprecedented act that asserted a monarch was not above the law. He refused to enter a plea, denying the court's legitimacy, but was convicted and executed ten days later, a shockwave felt across European monarchies.
No sitting English monarch had ever been formally tried by his own subjects before. After years of civil war between Charles I's royalist forces and Parliament's New Model Army, Oliver Cromwell and his allies determined that reconciliation with the king was impossible and established a High Court of Justice composed of 135 commissioners, though only around 68 ultimately took part in judgment.
When Charles was brought before the court in Westminster Hall on January 20, he refused to remove his hat or acknowledge the tribunal's authority, arguing that no earthly court could try a king, who answered to God alone. His silence and refusal to plead were themselves radical: the court eventually treated his silence as an admission and proceeded regardless.
The trial's audacity reverberated across Europe, where absolute monarchy was still the unquestioned order. Charles was convicted of high treason and beheaded on January 30, 1649, outside the Banqueting House at Whitehall, in one of the most consequential political executions in Western history, briefly transforming England into a republic.