The poet refers to "twenty centuries of stony sleep" and remarks that "The blood-dimmed tide is loosed, and everywhere /
A line from its second stanza is an allusion to the introduction of the poet's play The Resurrection, which describes the manifestation of the sphinx image.  The poet refers to "twenty centuries of stony sleep" and remarks that "The blood-dimmed tide is loosed, and everywhere / The ceremony of innocence is drowned;"  Its first stanza famously ends "The best lack all conviction, while the worst / Are full of passionate intensity" and introduces the gyre, the poet's symbol for the cycle of history.  FTP, name this poem that parallel's Christ's return b William Butler Yeats.
A line from its second stanza is an allusion to the introduction of the poet's play The Resurrection, which describes the manifestation of the sphinx image.  
"The Second Coming"