Byron's journey (with Venice as its proclaimed destination) took him to the field of the battle of Waterloo, and on down the Rhine to Switzerland. This was to be the trajectory of Childe Harold III. He spent the notoriously wet summer of 1816 in Switzerland, based at Cologny on Lake Geneva, in a house known as the Villa Diodati. He also spent some weeks touring in the Bernese Alps. Intensely influenced by his surroundings, it was over this period that he wrote most of the first draft of Manfred, as well as a number of significant shorter poems, including Prometheus and The Prisoner of Chillon. He did not of course know that hewould never return to England, but nevertheless he sensed that his departure marked a clear end to something. Alongside this sense of bridges burned and (a non-existent) Paradise Lost, perhaps the most important fact of the retrospectively crucial summer of 1816 is Byron's friendship with the poet Percy Bysshe Shelley. Only Byron's arrival in Italy the same autumn and his stay in Venice are as significant for his poetic development.

Percy Shelley and his young second wife Mary, the daughter of the radical thinker William Godwin and the equally radical feminist Mary Wollstonecraft, were travelling in the company of Mary's half-sister Claire Clairmont, who shortly before their departure from England had become one of Byron's lovers. Indeed, Claire knew by the time her party arrived at Geneva, shortly before Byron's, that she was pregnant. The Shelleys took a house atMontalègre, very near Cologny. Although Byron was more than somewhat wary of Claire's intentions, the two households spent much time together (thus incidentally providing more scandal for other English tourists to feed back to Britain). Famously it was a joint ghost-story writing competition, to pass the time in the bad weather, which led to Mary's writing Frankenstein.

Despite the presence of a sort of amanuensis in the person of Byron's doctor, John Polidori, it is an irritating fact that little of the substance of the two poets’ conversations is recorded. But the mutual influence is obvious in general terms, if difficult to pin down in detail.