Saint David's Day is the feast day of Saint David, the patron saint of Wales, and falls on 1 March, the date of Saint David's death in 589 AD. The feast has been regularly celebrated since the canonisation of David in the 12th century (by Pope Callistus II), though it is not a national holiday in the UK.

Traditional festivities include wearing daffodils and leeks, recognised symbols of Wales and Saint David respectively, eating traditional Welsh food including cawl and Welsh rarebit, and women wearing traditional Welsh dress. An increasing number of cities and towns across Wales including Cardiff, Swansea and Aberystwyth also put on parades throughout the day.

From Wikipedia