March 1 is the feast day of the patronal saint of Wales, Saint David (or Dewi Sant in Welsh). He was a sixth-century monk and later Archbishop of Wales, said to have converted thousands from the pagan Celtic tribes to Christianity. St. David's Cathedral in Pembrokeshire was built after he was made a saint in the twelfth century, on the site of one of his monasteries. He is usually depicted in art with a dove on his shoulder or hovering near him, and he is also closely associated with water, as fresh springs are said to have erupted in the Welsh countryside to mark many of the milestones of his life.
There are hymns specifically written for Saint David, many probably untranslated into English. You can see one at this page (of uncertain provenance) with several other legends about his life and works. However, I thought I would take this day of Welsh celebration to gather together several of the Welsh hymn tunes already used here over the last three years. The tunes of Wales were said to be rousing melodies, some from older folk melodies, simple for a congregation to learn and remember, and were not from a high church tradition. This is probably still true today - you will probably know many of these even if you did not see them the first time around on the blog. I like them all.
These are most, if not all, of the Welsh tunes I've used, and I'm sure there are more to come (the familiar AR HYD Y NOS has not yet appeared, for example).
St. David's Day is also an occasion for large gatherings of Welsh choirs, particularly in the male choir tradition, and many of these hymn tunes were probably sung somewhere today. If you want to hear more of these tunes, searching for any of the tune names above at YouTube will probably bring up a rendition or two (or more) sung exuberantly by a Welsh male choir.
P.S. - Our commenter Leland is looking for some information on a particular Welsh hymn (the text, not the tune) at his blog, if anyone here happens to know more about it.