What are the classical Greek allusions in John Keats's "To Autumn"?

Keats wrote the poem "To Autumn" late in his poetic
career, and it has been referred to as one of the most perfect poems in the English
language.  The poem consists of three stanzas.  The first stanza references the bounty
of early autumn before the harvest, the second personifies Autumn as a harvester, though
one in stasis, and the third stanza describes the chilly end of the season and the
promise of winter, which is also the promise of death.

The
personification of Autumn could be considered an allusion to the mythology of ancient
Greece.  However, compared with his other odes, "Ode to a Grecian Urn" and "Ode to
Psyche,"  this poem does not include as many overt allusions to ancient Greece.  Rather,
the poem subtly recalls the myth of Persephone, Demeter, and Hades.  In this myth,
Demeter, the goddess of the earth, casts the land into a permanent winter when her
daughter, Persephone, is kidnapped by Hades.  Persephone is eventually able to return
from the underworld, but only for half the year.  In celebration, Demeter brings Spring
and Summer to the land.  But when her daughter must return to the world of the dead,
Demeter brings death to the earth in the form of Autumn and
Winter.

Keats's poem offers up an acceptance of this cycle
of life and death.  In the final stanza, the speaker addresses a personified Autumn by
saying:

Where
are the songs of Spring?  Ay, where are they?

Think not of
them, thou hast thy music
too

By noting this, the
speaker realizes that the approach of death brought by Autumn can be just as beautiful
as the promise of life found in the Spring.