Obsessive rantings and brooding visions

BLAKE'S JERUSALEM
Fitzwilliam Museum, Trumpington Street, Cambridge University. Until May 14

William Blake's most famous lyric, Jerusalem , is a heartfelt protest against the failures of spirituality and politics in newly industrial Britain. One of the grimmest ironies of literary history is that this, of all poems, should have become first a pious hymn, beloved of the church establishment the poet so detested, and then, in a final insult, the rallying cry for the baying rugby crowd at Twickenham. Blake saw himself as a prophet pleading with England to escape from the "mind-forg'd manacles" of institutional religion. To have written a public schoolboys' hymn would be for him a total nightmare.

The celebrated lines of Jerusalem were just the beginning of Blake's obsession with the spiritual state of the nation and his longing for the lost ideal of the heavenly city. Through the years 1804-18 he wrote a long, rambling poem called Jerusalem: The Emanation of the Giant Albion .

His aim was "to speak to future generations by a Sublime Allegory", and he was certain of his poem's status. "I consider it as the Grandest Poem that This World contains," he wrote. Blake's mental state was extremely fragile throughout this period. His self-proclaimed masterpiece has remained almost entirely unread, even in the scholarly community. This is not surprising: it is full of bizarrely named characters exhorting each other to greater spiritual fervour, allegorical representations of his personal enemies and the baroque sufferings of the hero Albion, who stands for England. It is an obsessive, ranting and tedious outpouring.

Blake illustrated the four chapters of The Emanation of the Giant Albion with 100 plates. There is only one complete copy of these coloured prints, now at Yale. The Fitzwilliam Museum has collected together the 25 illustrated pages of the first chapter, together with four alternative sketches. It makes for a fascinating, if short, exhibition. Anyone interested in Blake or in the history of 19th-century art should take the rare opportunity of seeing these pages together.

The poem itself is written in Blake's familiar hand and printed in the rusty colour of dried blood. In the margins of several pages there are allegorical figures from the poem. Jerusalem is represented as a naked woman. Albion himself appears as a naked, muscular man, in one vivid image tortured and lacerated by his enemies - symbolic figures of repression and malice. The images are brooding, obsessive and difficult.

These pictures are unlike anything else in early 19th-century art. But they strikingly anticipate 20th-century art and design, especially the world of graphic novels, with its roots in modernist and surrealist painting. Blake's poetic prophecies may be unheard, but his art is truly prophetic. The exhibition adds three other Blake volumes, The Songs of Innocence and Experience , The Daughters of Albion and The Marriage of Heaven and Hell . This reveals the poet's descent into the private world of his fantastic visions. Also on show are a handful of contemporary volumes by other authors and illustrators, exhibited in order to present something of the political background to Blake's revolutionary zeal.

This material barely helps us understand his fervour, and the commentary provided in the exhibition is very thin. We are invited just to look at the pictures. They are troubling and memorable drawings. But a wider intellectual framing would have made the show more stimulating.

Simon Goldhill is professor in Greek literature and culture at Cambridge University and author of The Temple of Jerusalem , published by Profile, Pounds 8.99.