Firstly let us start by clearing up the name:
As both armies prepared for battle the following morning an image appeared in the sky of a white cross. The image encouraged the Picts and frightened the Northumbrian army who fled in panic. The site of the battle is known as Athelstanford after the Northumbrian leader who was killed in the battle. From then onwards the Saltire has been used as Scotland’s National Flag .
The Saltire is also referred to as St Andrews Cross and as you may know he is the patron saint of Scotland. What you may not know is that he is also the patron saint of Romania and Russia. St Andrew was a fisherman from Galilee and a brother of Simon (Peter) - one of the first Disciples of Christ. He was crucified by the Romans at Patras in 69 AD. The legend of the St Andrews cross came from the fact that feeling unworthy of a crucifixion similar to that of Christ he demanded to be crucified on an X shaped cross.
His remains were entombed in Constantinople but later removed by St Rule who was told to take the remains to the (ends of the earth) for safe keeping. He took a tooth, an arm bone, a kneecap and some fingers from the tomb and set off for the most remote place he could find. That place was on the east coast of Scotland and has become known as St Andrews. The relics were later destroyed during the Reformation and most of the other remains were stolen from Constantinople and moved to Amalfi in Italy. Some of these relics were presented to Scotland in 1879 and 1969.