Endymion

Endymion is a poem by John Keats first published in 1818. Keats based the poem on the Greek myth of Endymion, the shepherd beloved of the moon goddess Selene. The poem elaborates on the original story and renames Selene "Cynthia" (an alternative name for Artemis). The poem is written in rhyming couplets in iambic pentameter (also known as heroic couplets).
Keats dedicated this poem to the late poet Thomas Chatterton.
The poem begins with the famous line "A thing of beauty is a joy for ever". (Summary by Alan Mapstone and Wikipedia)