Begun some time around 1797, Vala or The Four Zoas is William Blake's great unfinished masterpiece, an attempt to provide a complete mythology of Blake's universe of characters, Urizen, Los, Orc, Vala and many more. The poem has fascinated and perplexed readers ever since and, in this episode of Visionary, Professor Jason Whittaker is joined by Dr Annise Rogers who has worked in detail on Blake's epic. They discuss the conditions in which the poem was written, as well as provide some explanation as to its characters and significance.