Which royal ceremony was the Gunpowder Plot meant to attack in 1605?

The Gunpowder Plot was meant to attack the State Opening of Parliament.

The conspirators planned to place explosives beneath the House of Lords and detonate them when King James VI and I, members of Parliament and other senior figures gathered for the ceremony on 5 November 1605. Their immediate aim was to kill the king and destroy the political and religious leadership of Protestant England.

The plot was led by Robert Catesby, with Guy Fawkes assigned to guard the gunpowder in the cellars beneath Westminster. After the plot failed, the conspirators hoped to spark a wider revolt and place the king’s daughter, Elizabeth, on the throne as a Catholic ruler.

The State Opening is therefore more precise than simply saying the plot targeted Parliament: the planned explosion was timed for the ceremony that formally opened the parliamentary session. A lasting reminder survives in the ceremonial search of the Palace of Westminster’s cellars before the State Opening, a practice derived from the discovery of Fawkes and the explosives.