The Elgin Marbles inspired Keats to write-

He was inspired to write the poem after reading two articles by English artist and writer Benjamin Haydon. Keats was aware of other works on classical Greek art, and had first-hand exposure to the Elgin Marbles, all of which reinforced his belief that classical Greek art was idealistic and captured Greek virtues, which forms the basis of the poem. (The Elgin Marbles are a collection of Classical Greek marble sculptures made under the supervision of the architect and sculptor Phidias and his assistants.)