Mirie it is while sumer ilast Merry it is while summer ylast is a Middle English song from the first half of the 13th century. It is about the longing for summer in the face of the approaching cold weather. It is one of the oldest songs in the English language and one of the few examples of non-liturgical music from medieval England.

https//en.wikipedia.org/wiki/Mirie_it_is_while_sumer_ilast#References