On the 12th of March, 1818, Shelley quitted England, never to return. His principal motive was the hope that his health would be improved by a milder climate; he suffered very much during the winter previous to his emigration, and this decided his vacillating purpose. In December, 1817, he had written from Marlow to a friend, saying:
’My health has been materially worse. My feelings at intervals are of a deadly and torpid kind, or awakened to such a state of unnatural and keen excitement that, only to instance the organ of sight, I find the very blades of grass and the boughs of distant trees present themselves to me with microscopic distinctness. Towards evening I sink into a state of lethargy and inanimation, and often remain for hours on the sofa between sleep and waking, a prey to the most painful irritability of thought. Such, with little intermission, is my condition. The hours devoted to study are selected with vigilant caution from among these periods of endurance. It is not for this that I think of travelling to Italy, even if I knew that Italy would relieve me. But I have experienced a decisive pulmonary attack; and although at present it has passed away without any considerable vestige of its existence, yet this symptom sufficiently shows the true nature of my disease to be consumptive. It is to my advantage that this malady is in its nature slow, and, if one is sufficiently alive to its advances, is susceptible of cure from a warm climate. In the event of its assuming any decided shape, it would be my duty to go to Italy without delay. It is not mere health, but life, that I should seek, and that not for my own sake—I feel I am capable of trampling on all such weakness; but for the sake of those to whom my life may be a source of happiness, utility, security, and honour, and to some of whom my death might be all that is the reverse.’
In almost every respect his journey to Italy was advantageous. He left behind friends to whom he was attached; but cares of a thousand kinds, many springing from his lavish generosity, crowded round him in his native country, and, except the society of one or two friends, he had no compensation. The climate caused him to consume half his existence in helpless suffering. His dearest pleasure, the free enjoyment of the scenes of Nature, was marred by the same circumstance.
He went direct to Italy, avoiding even Paris, and did not make any pause till he arrived at Milan. The first aspect of Italy enchanted Shelley; it seemed a garden of delight placed beneath a clearer and brighter heaven than any he had lived under before. He wrote long descriptive letters during the first year of his residence in Italy, which, as compositions, are the most beautiful in the world, and show how truly he appreciated and studied the wonders of Nature and Art in that divine land.