The oldest song for which we have the music is that Top Ten Hit from 1215, Sumer is icumen in. Since tomorrow is May-Day (and the notional beginning of summer in Merrie England), I offer it now as my thirtieth and last poem for National Poetry Month, 2008:
Sumer is icumen in, Lhude sing cuccu! Groweth sed and bloweth med And springth the wode nu. Sing cuccu! Awe bleteth after lomb, lowth after calve cu; bulluc sterteth, bucce verteth, murie sing cuccu! Cuccu! Cuccu! Wel singest thu cuccu, ne swik thu naver nu.