"And did those feet in ancient time" is a poem by William Blake from the preface to his epic Milton: A Poem in Two Books, one of a collection of writings known as the Prophetic Books. The date of 1804 on the title page is probably when the plates were begun, but the poem was printed c. 1808 Today it is best known as the hymn "Jerusalem", with music written by Sir Hubert Parry in 1916. The famous orchestration was written by Sir Edward Elgar. It is not to be confused with another poem, much longer and larger in scope, but also by Blake, called Jerusalem The Emanation of the Giant Albion.

The poem was supposedly inspired by the apocryphal story that a young Jesus, accompanied by Joseph of Arimathea, a tin merchant, travelled to what is now England and visited Glastonbury during his unknown years. That has been questioned, e.g. by A.W. Smith, who concluded that "that there was little reason to believe that an oral tradition concerning a visit made by Jesus to Britain existed before the early part of the twentieth century". The poem's theme is linked to the Book of Revelation (3:12 and 21:2) describing a Second Coming, wherein Jesus establishes a New Jerusalem. Churches in general, and the Church of England in particular, have long used Jerusalem as a metaphor for Heaven, a place of universal love and peace.[a]

In the most common interpretation of the poem, Blake implies that a visit by Jesus would briefly create heaven in England, in contrast to the "dark Satanic Mills" of the Industrial Revolution. Blake's poem asks four questions rather than asserting the historical truth of Christ's visit. Thus the poem merely implies that there may have been a divine visit, when there was briefly heaven in England.

"Dark Satanic Mills"
Albion Flour Mills, Bankside, London

The phrase "dark Satanic Mills", which entered the English language from this poem, is often interpreted as referring to the early Industrial Revolution and its destruction of nature and human relationships. This view has been linked to the fate of the Albion Flour Mills in Southwark, the first major factory in London. This rotary steam-powered flour mill by Matthew Boulton and James Watt could produce 6,000 bushels of flour per week. The factory could have driven independent traditional millers out of business, but it was destroyed in 1791 by fire, perhaps deliberately. London's independent millers celebrated with placards reading, "Success to the mills of Albion but no Albion Mills." Opponents referred to the factory as satanic, and accused its owners of adulterating flour and using cheap imports at the expense of British producers. A contemporary illustration of the fire shows a devil squatting on the building. The mills were a short distance from Blake's home.

Blake's phrase resonates with a broader theme in his works, what he envisioned as a physically and spiritually repressive ideology based on a quantified reality. Blake saw the cotton mills and collieries of the period as a mechanism for the enslavement of millions, but the concepts underpinning the works had a wider application

Another interpretation, amongst Nonconformists, is that the phrase refers to the established Church of England. This church preached a doctrine of conformity to the established social order and class system, in contrast to Blake. In 2007 the new Bishop of Durham, N. T. Wright, explicitly recognised this element of English subculture when he acknowledged this alternative view that the "dark satanic mills" refer to the "great churches". In similar vein, the critic F. W. Bateson noted how "the adoption by the Churches and women's organizations of this anti-clerical paean of free love is amusing evidence of the carelessness with which poetry is read".

Stonehenge and other megaliths are featured in Milton, suggesting they may relate to the oppressive power of priestcraft in general; as Peter Porter observed, many scholars argue that the "[mills] are churches and not the factories of the Industrial Revolution everyone else takes them for". An alternative theory is that Blake is referring to a mystical concept within his own mythology related to the ancient history of England. Satan's "mills" are referred to repeatedly in the main poem, and are first described in words which suggest neither industrialism nor ancient megaliths, but rather something more abstract: "the starry Mills of Satan/ Are built beneath the earth and waters of the Mundane Shell...To Mortals thy Mills seem everything, and the Harrow of Shaddai / A scheme of human conduct invisible and incomprehensible"