In Book ii of Chaucer’s Troilus and Criseyde, when Pandarus sets out for Criseyde’s house to persuade her to reciprocate Troilus’s love, the narrator declares: ‘Now Janus, god of entree, thow hym gyde!’ Janus, the Roman god of entrances and exits, was commonly depicted with two faces, one looking forward and one looking back, an image which is suggestive of the poetic technique of Geoffrey Chaucer. He is a poet who hovers on the threshold, glancing back at the landscape of his literary forebears, but looking determinedly forward into his own poetic House of Fame. Centuries later, when William Blake painted the Canterbury Pilgrims, he placed Chaucer, ‘the great poetical observer of men’, at the far right of the picture enclosed in the gothic archway of the Tabard Inn, about to set forth on the road ahead of him. Blake saw in The Canterbury Tales ‘characters which compose all ages and nations’; they represented the ‘physiognomies … of universal human life’. But in the fourteenth century Chaucer was venturing into new and potentially treacherous territory. He brought together characters and genres which had not shared the same poetic space before and he stretched the linguistic potential of the vernacular to its limits. Yet his apprenticeship for his role as ‘Father of English Poetry’, as Dryden was famously to dub him, began with dream visions in which he used contemporary dream theory such as Macrobius’s Commentary on the Dream of Scipio to explore what it meant to be an English poet.