Charles I was executed outside the Banqueting House at Whitehall on 30 January 1649. He had lost the Civil War, lost effective power and then lost the claim that those beneath him could not judge a king.

His death was public. That was part of the point.

Charles had not been killed quietly after defeat. He was brought to trial before a specially created High Court of Justice, charged as a traitor and held responsible for the bloodshed of the wars. The charge itself marked a political break. Treason was normally understood as a crime against the king. In January 1649, the king was accused of treason against his own people.

Charles refused to accept the court’s authority. He did not simply deny the charge. He denied that the court had any lawful right to try him. In his view, kingship placed him beyond such judgment. The court claimed the opposite: that the king could be called to account when his rule had brought war on the kingdom.

That clash gave the trial its force. It was about Charles’s actions, but it was also about where authority lay. If the king was answerable to a court created by his opponents, the monarchy no longer stood above political judgment. If he was not answerable, the trial was an unlawful force given legal form.

The process was not a calm act by a united Parliament. The House of Lords rejected the trial. Many MPs had already been excluded after Pride’s Purge. The authority behind the court was narrow, disputed and backed by the army. That does not make the execution a private killing. It does mean the event should not be treated as Parliament calmly judging the crown.

On the scaffold at Whitehall, the dispute became visible. Charles was beheaded outside the Banqueting House, a building closely linked with the court culture of his father and the royal image of the Stuart monarchy. The setting made the act hard to mistake for anything else. This was the formal killing of a king in the centre of government.

For those who supported the execution, it was justice after years of war. For those who rejected it, it was regicide and a violation of the monarchy itself. The same blow could be read as a lawful judgment or as murder. The country did not agree on what it had seen.

The consequences came quickly. Charles’s personal rule was over, but more than one man had been removed. The monarchy was abolished. The House of Lords was abolished. England moved towards the Commonwealth, a republic that still had to work out how power would be held, justified and enforced.

30 January 1649 was more than the death of Charles I. It showed that the monarchy had failed as the prevailing political settlement. A king had been tried, condemned and killed in public. What replaced him was still uncertain.