In The Marriage of Heaven and Hell he gave a definitive opinion of the presence of churches (on Plate 11):
The ancient Poets animated all sensible objects with Gods or Geniuses, calling them by the names and adorning them with the properties of woods, rivers, mountains, lakes, cities, nations, and whatever their enlarged & numerous senses could percieve.
And particularly they studied the genius of each city & country, placing it under its mental deity.
Till a system was formed, which some took advantage of & enslav'd the vulgar by attempting to realize or abstract the mental deities from their objects; thus began Priesthood.
Choosing forms of worship from poetic tales.Re that system he had this to say:
And a length they pronounc'd that the Gods had order'd such things.
Thus men forgot that All deities reside in the human breast.
" I must Create a System, or be enslav'd by another Mans
(Jerusalem 10.20; Erdman 153)