Sumer Is Icumen In (Anonymous c. 1225)

This is the oldest song in existence of its kind, called a Rondellus (a round accompanied by an ostinato bass part).  It is written in mensural notation and is a manuscript from Reading Abbey (a collection of various texts, songs, etc.).  Interestingly Sumer is icumen in is the only english piece in the manuscript.  It is very pleasant and interesting to listen to.  In this version there is an instrumental accompaniment of fiddles, droning bagpipe-like sounds, and a plucked instrument.  However, it is possible to perform this work entirely a capella, and that might be the way it was meant.  We don't really know for sure.  The song builds to a climax in which four different voice parts come in, one after another, while two other singers are doing the ostinato.  The text is in an old style of english that makes it somewhat unintelligible today, but many of the words are close enough to guess at what they might mean.  The title would be "Summer is coming in" in modern english.
Here is the the text:

Sumer is icumen in,
Lhude sing cuccu!
Groweþ sed and bloweþ med

And springþ þe wde nu,
Sing cuccu!
Awe bleteþ after lomb,
Lhouþ after calue cu.
Bulluc sterteþ, bucke uerteþ,
Murie sing cuccu!
Cuccu, cuccu, wel þu singes cuccu;

Ne swik þu nauer nu.
Pes:

Sing cuccu nu. Sing cuccu.
Sing cuccu. Sing cuccu nu!

Note: Pes indicates what is sung by the bass ostinato parts.