A remarkable story of stoicism, giving a lesson to us all.
It is believed that the apostle Andrew was crucified on a saltire (X-shaped) cross; hence the name St. Andrew's Cross. He is said to have told his executioners that he was not worthy to be crucified on the same cross style as Jesus, and persuaded them to alter the shape. If this is true, it's a remarkable example of stoicism displayed by a man, no doubt beaten and starved, yet retaining the mental energy to plead such a thing with his brutal executioners. Detailed records of his crucifixion only date back to the Middle Ages, and these records are influenced be the imagination of the medieval artists. But even if the origin is a myth, the cross shape reminds Christians that they should exercise humility.
Before Peter was crucified, he too requested that a cross different to Christ's Latin Cross be used. Therefore we have another cross that Christians associate with humility; the upside-down Latin Cross, known as St. Peter's Cross.
In Greek, the first letter for Christ (Chi) also happens to be 'X'-shaped, as in the Chi Rho Cross. An alternative name for Christmas is Xmas, a valid abbreviation although rejected by some as being a commercial attempt to remove Christ from Christmas, by crossing Him out. (Curiously, Xmas is often shown as X'mas in Japan. See St. Nicholas Cross and Christmas in Japan.)
Instead of simply saying that something is 'X-shaped' or 'saltire', the term 'St. Andrew's Cross' is used for several items that have absolutely nothing to do with St. Andrew or even religion. For example, there's argiope kiyserlingi and the argiope mangal - a tiny, brightly striped spider found in the mangroves of Singapore. These are commonly known as 'St. Andrew's Spiders' because they hold their eight legs in pairs, forming an X shape. Then there's the hypericum hypericoides, a small shrub of the St. John's-wort family. Its flowers form a cross with their four yellow petals and is known as 'St. Andrew's Cross'.
The St. Andrew's Cross is seen on the American Confederate flag, showing the Scottish lineage of many Southerners. On this flag it is known as the Southern Cross. It is also seen on several national flags. For example the white cross on a blue background as the flag of Scotland, and a red cross on a white background as St. Patrick's Cross of the Irish. Both of these crosses were superimposed on England's red cross on a white background, St. George's Cross, to give the United Kingdom's Union Flag ('Union Jack') (...often taught to Boy Scouts as something that might be useful to know one day. They are also taught how this cross is used in mathematics to multiply numbers)
The saltire on the flag of Scotland is called 'St. Andrew's Cross' and its colours are said to come from a white cross made by clouds in the blue sky. In the ninth century, King Angus saw this arrangement on the day before a decisive battle over the English Northumbrian Angles command by Athelstan. King Angus considered it to be a good omen and won the battle. (See also Constantine's Cross.)
Merkill was the place where King Angus' army of Picts and Scots were fighting the King Athel's army of Sassenachs from Northumbria. One night, Angus prayed to God for help in the next day's battle. A vision of Saint Andrew appeared to him, promising victory. The next day, King Angus' men saw two long white clouds streaking across the blue sky forming a cross. They took this as a sign from Saint Andrew and were sufficiently roused to beat the lowlanders in the battle.
Of course, the sign could have been meant for King Athel's men, but perhaps they were too busy fighting to be looking up at the sky. Or were these long clouds the exhaust of jet engines from some early alien visitation? Or 'earthquake clouds'? Whatever interpretation we wish to make, the Scots believed it was nothing less than a miracle. This battle took place just a stone's throw from Markle, East Lothian, Scotland. Markle village has now gone, but a few ruins remain (for example Markle Castle). The original name of the place was Merkill, and this might have come from the word miracle. The white cross on blue background was adopted as the flag of Scotland and St. Andrew became Scotland's Saint.
It is of no surprise therefore that the Church of Scotland uses the St. Andrew's Cross as the background of their main emblem, which also depicts the miraculous burning bush that was not consumed (Exodus 3). The burning bush symbol is repeated in the emblems of the Presbyterian Churches around the world and represents the bondage of the church in Egypt. Their emblems remind us that the church and its people, in every age and every culture, may suffer severe persecution. And yet God prevents His people from being destroyed. An alternative interpretation is that the fire of the Holy Spirit can burn away the sin and leave the soul pure. The burning bush symbol was also used by the early Huguenots.
A variation of the St. Andrew's Cross is the Burgundy Cross and all these crosses represent the Christian religion of the kings at the time the flags were made. Other national flags have an 'X' cross, but these have no Christian basis. The flag of Burundi for example, where even though the country is nominally 'Christian', the white cross is not used as a religious symbol. It is a symbol of peace - the goal of everyone after years of ethnic violence between Hutu and Tutsi factions. The flag of Grenada just happens to have a cross made by the four triangles of wisdom, warmth, vegetation and agriculture. The yellow/gold cross on the Jamaican flag signifies sunshine, as with the Macedonian flag.
There is a variation of St. Andrew's cross on the flag of the Vatican (see also Papal Cross). Since the 14th century, two crossed keys have been the official insignia of the Holy See. These keys are the symbols of St. Peter (popes are considered direct descendants of St. Peter's office). The keys were given to Peter (see Matthew 16:19) by Christ to open the doors to paradise, just as the cross opens the gates of heaven for those who believe in Him.
But what does the St. Andrew Cross mean for us today? See the meaning of the cross and also read Humility and Sacrifice by Rev. David Linde.