Saint David, the patrion Saint of Wales, is celebrated on March 1st.
St. David was a Celtic monk who lived about 100 years after the Romans left the British Isles. Little is known for sure about him, due to both the amount of time that has past and that no real records where kept. He was known to be very strict but also fair. Known for spreading the gospel and living a very frugal life, he is looked upon as an ideal to live up too. The most famous story tells of him giving a speech to a large group of people at Synod of Llanddewi Brefi, where to allow him to be heard and seen the ground raised beneath his feet.
David became a Saint in 1120 and thus his day was recorded in the church records.
Today St. David’s Day is celebrated through out Wales and any where there are those of Welsh decent. The most common tradition is that of wearing either leeks for men and daffodils for women. Also in Wales girls wear the traditional Welsh dress. Many individual events take place during the day and schools at one time would let out for half a day, but this practices is no longer supported by the national government. There is also a large parade in Cardif.
National History Museum of Wales http://www.museumwales.ac.uk/en/275/
Nice article http://www.davidmorgan.com/stdavid.html
Another nice article http://www.sucs.swan.ac.uk/~rhys/stdavid.html