Scots Wha Hae

The lyrics were written by Robert Burns in 1793, in the form of a speech given by Robert the Bruce before the Battle of Bannockburn in 1314, where Scotland maintained its sovereignty from the Kingdom of England. Although the lyrics are by Burns, he wrote them to the traditional Scottish tune 'Hey Tuttie Tatie' which, according to tradition, was played by Bruce's army at the Battle of Bannockburn, and by the Franco-Scots army at the Siege of Orleans.

Reference: Wikipedia