The Garden of Love

Question

I went to the Garden of Love,
And saw what I never had seen;
A Chapel was built in the midst,
Where I used to play on the green.

And the gates of this Chapel were shut
And "Thou shalt not," writ over the door;
So I turned to the Garden of Love
That so many sweet flowers bore.

And I saw it was filled with graves,
And tombstones where flowers should be;
And priests in black gowns were walking their rounds,
And binding with briars my joys and desires

The question is what literary devices are used?

I can see that imagery is used and possibly allegory? Am i missing anything else?