The date of March 1 was chosen in remembrance of the death of Saint David on March 1, 589, and has been celebrated by followers since then. The date was declared a national day of celebration within Wales in the 18th century.
Many Welsh people wear one or both of the national emblems of Wales on their lapel to celebrate Saint David: the daffodil (a generic Welsh symbol which is in season during March) or the leek (Saint David's personal symbol) on this day.
The Flag of Saint David is most commonly seen flying on Saint David's Day.