On August 18, 1648, with no relief from the siege in sight, the royalist garrison holding Colchester Castle surrendered and Oliver Cromwell's army firmly ended the rule of Charles I of England. To send a clear message to the fallen monarch, the rebels executed four of the senior officers captured at the castle. Yet still, the king refused to accept he had lost the war. As France and other allies mobilized in support of Charles, a tribunal was hastily...