Elizabeth II may be the undoubted sovereign of the United Kingdom, but there is one place where even she is not in charge. In fact, she may not even set foot in it. That place is the House of Commons.

The curious custom dates back to the last time a monarch set foot in the chambers: January 4, 1642. On that day Charles I forced himself into the House, along with armed soldiers, intent upon arresting five Members of Parliament.

When the king demanded the location of the men whom he sought, the House Speaker, William Lenthall, refused. He said, “May it please your Majesty, I have neither eyes to see nor tongue to speak in this place but as the House is pleased to direct me, whose servant I am here.”

Charles’ actions touched off the English Civil War and the temporary abolition of the British monarchy. Although the monarchy was eventually restored, no king or queen has since dared violate the authority of the House of Commons by setting foot in its chambers since.

At each State Opening of Parliament, this tradition is remembered and reinforced when the monarch’s representative, Black Rod, has the door to the House of Commons slammed in his face when he attempts to summon the Members to the chambers of the House of Lords to hear the monarch’s speech.