The use of gun salutes for military occasions is traced to early warriors who demonstrated their peaceful intentions by placing their weapons in a position that rendered them ineffective. Apparently this custom was universal, with the specific act varying with time and place, depending on the weapons being used. A North African tribe, for example, trailed the points of their spears on the ground to indicate that they did not mean to be hostile. The tradition of rendering a salute by cannon originated in the 14th century as firearms and cannons came into use. Since these early devices contained only one projectile, discharging them once rendered them ineffective. Originally warships fired seven-gun salutes–the number seven probably selected because of its astrological and Biblical significance. Seven planets had been identified and the phases of the moon changed every seven days. The Bible states that God rested on the seventh day after Creation, that every seventh year was sabbatical and that the seven times seventh year ushered in the Jubilee year. Land batteries, having a greater supply of gunpowder, were able to fire three guns for every shot fired afloat, hence the salute by shore batteries was 21 guns. The multiple of three probably was chosen because of the mystical significance of the number three in many ancient civilizations. Early gunpowder, composed mainly of sodium nitrate, spoiled easily at sea, but could be kept cooler and drier in land magazines. When potassium nitrate improved the quality of gunpowder, ships at sea adopted the salute of 21 guns. The 21-gun salute became the highest honor a nation rendered. Today the national salute of 21 guns is fired in honor of a national flag, the sovereign or chief of state of a foreign nation, a member of a reigning royal family, and the President, ex-President and President-elect of the United States. It is also fired at noon of the day of the funeral of a President, ex-President, or President-elect.