Introductions to marches vary but some standard practices include: (a) "tutti" unison ("The Washington Post"), (b) "tutti" rhythmic unison with contrary motion ("The Thunderer"), (c) "tutti" rhythm unison in four-part harmony ("Semper Fi"), and (d) four-part independent ("The Klaxon"). The introduction is commonly based on the dominant key to create clarity of key as centered in the first strain, (see harmonic progressions below). Generally, the intro is not repeated, but it is in some marches: "Bravura", "The Rifle Regiment", and "Washington Grays". The introduction generally starts in major because marches typically are in major keys, but there are marches with introductions in minor keys, including "Gladiator", "The Picadore", "Nobles of the Mystic Shrine", and "Rolling Thunder".