As far as I know, only the great Yeats thought of eternity as some kind of artifice or construct of the "drowsy emperor."
I was wondering if anyone knows of any other poets who might have held this idea before Yeats. I expect a poet as great as Yeats to have ideas which may be soley his own. This could be one. It is easy to miss ideas like this, to read right over them. I read over this passage many times for years before its meaning jumped out at me. I have always found everything about the poetry of Yeats stirring, though. Blake had quite an influence on Yeats. I wonder if this is an idea Blake held.