According to legend, in the year 832 BC. e. Angus King II, who led the army of the Picts and Scots, before the battle with England, which led Æthelstan, the night before the battle he prayed to God for the victory on the battlefield, and made a vow that if he wins announce St. Andrew the patron saint of Scotland. In the morning clouds over the battlefield formed on blue sky letter "X" follows the shape of the cross on which 70 AD. e. in the Greek city of Patras was crucified Apostle Andrew. The Picts and Scots were encouraged by this divine omen, and England was thrilled. As a result, the army Angus II, inferior to the number of troops Angles, win the battle and the Holy Apostle Andrew was declared the patron saint of Scotland.
In fact, the first use of an oblique image of the cross as a national symbol, appeared only in print Scottish Guard in 1286, and the emergence of the flag refers to 1542.
In 1601, the flag of Scotland was united with England flag in the flag of Great Britain