Bronze orpheus sings 

could you tell me why it is called bronze orpheus?
here the text:
bronze orpheus crosses the field,
playing a guitar without strings.
he's called up springtimes and winds
and now pours his grief in the stream.
 
none of the winds or springtimes,
          not even the hungry shepherd knows
whether to grieve along or head back home.
 
his weeping bronze wails for eurydice
raise a song like fish pounding the water.
mischievous sunglints run through the grass.
a lazy day swings in the trees.
 
a colony of ants finishes building
its heaven-domed home in happy calm