139. Who is Black Rod?
His full title is Gentleman Usher of the Black Rod, and he ranks high among the officials of the Court, coming under the Lord Chamberlain. His name or title comes from the ebony stick he carries as a badge of his office and which is surmounted by a gold lion. His office dates from the foundation of the Order of the Garter in 1348, and he is the usher of that Order. He attends for the most part upon Parliament, and one of his chief duties is to bear messages from the House of Lords to the House of Commons. When he goes ceremonially to the House of Commons, the door is always slammed in his face, and he must then knock and announce his errand. The reason for this is that once King Charles I went down to the House of Commons to arrest five members whom he regarded as obnoxious to him, and from that time no sovereign has entered the Commons.
L. G. Pine, Heraldry, Ancestry and Titles: Questions and Answers (108)