So sweet the hour, so calm the time,
I feel it more than half a crime,
When Nature sleeps and stars are mute,
To mar the silence ev'n with lute.
At rest on ocean's brilliant dyes
An image of Elysium lies:
Seven Pleiades entranced in Heaven,
Form in the deep another seven:
Endymion nodding from above
Sees in the sea a second love.
Within the valleys dim and brown,
And on the spectral mountain's crown,
Endymion was variously a handsome shepherd, hunter, or king who was said to rule and live at Olympia in Elis. He was supposedly the mortal son of Zeus whom Selene (Goddess of the Moon) fell in love with. 
 
 There is a bit of confusion on why he was put into an everlasting slumber. Some say it was a wish granted by Zeus so that he would stay eternally youthful. Other sources claim it was punishment to Selene for leaving her moon duties to visit him (or because poor Endymion was trying to lie with Zeus’s wife, Hera). Some say it was a wish granted by Zeus to Selene because she so loved to watch Endymion sleep and wanted him to stay young and alive forever.
Serenade