In 2001 three groups of the so-called ‘Satanic Mills’ described in Blake’s poem Jerusalem were designated as UNESCO World Heritage Sites. I’m no poet and I don’t claim to understand it fully, but the meaning of the poem is patently multi-layered, and becomes more opaque the deeper one delves.  On a literal level though we can understand, at least intuitively, the scorn which Blake heaped upon these dismal places due in part to the dreadful working conditions. To Blake, these buildings represented the mechanisation of human beings and a cold, unfeeling disregard for our nature, and stood in stark contrast to ‘England’s green and pleasant land’.  He saw this, roughly speaking, as a kind of tyranny and since he was a fairly radical Christian, he associated tyranny with the figure of Satan. Some alternative symbolism could be used here depending on your own worldview, but the essential point remains.