I think it's more a case of Led Zep creating a thematic feel to the song, rather than a literal reference to historical events, using their (by 1973) characteristic Celtic mythical content. The song seems to be about a small group of people, or an individual, that is being pursued by something that would wipe out everything in order to stop the message they carry - "a dream for me and you". Other commenters are right that it fits with historical moments of religious upheaval and change, but I think that's simply co-incidental.
I guess in modern terms, being "pursued mercilessly" might mean a moment of loss of identity as a group or individual, through illness or circumstances; or if you were in a modern band, being smothered by what society wanted from you and what you might want to do as an artist and you saw no compromise between the two. Ironically, the "pain" of watching everything you thought you were fall apart drives you forward to new artist creation.
I think it's more a case of Led Zep creating a thematic feel to the song, rather than a literal reference to historical events, using their (by 1973) characteristic Celtic mythical content. The song seems to be about a small group of people, or an individual, that is being pursued by something that would wipe out everything in order to stop the message they carry - "a dream for me and you". Other commenters are right that it fits with historical moments of religious upheaval and change, but I think that's simply co-incidental.
I guess in modern terms, being "pursued mercilessly" might mean a moment of loss of identity as a group or individual, through illness or circumstances; or if you were in a modern band, being smothered by what society wanted from you and what you might want to do as an artist and you saw no compromise between the two. Ironically, the "pain" of watching everything you thought you were fall apart drives you forward to new artist creation.