In this thesis I consider six poems which Shelley wrote in Italy, between 1818 and his death in 1822: Prometheus Unbound, The Cenci, "On the Medusa of Leonardo da Vinci in the Florentine Gallery", "Ode to the West Wind", Adonais, and The Triumph of Life. My chief aim is to examine Shelley's use of the Gothic in his endeavours to invoke the sublime and the numinous, my understanding of these terms being based, in general, on definitions given by Edmund Burke and Rudolph Otto respectively. I also study in detail the continuing presence of Gothic qualities in Shelley's work, from the time of his earliest poems and novels, and examine the origins of these Gothic elements not only as they appear in the works of Shelley's contemporaries such as Goethe, Matthew Lewis, William Beckford and Charles Brockden Brown, but also in the writings of earlier figures such as Spenser and Milton. In the poetry written during his time in Italy, it can be seen that Shelley also draws considerably on what can only be described as the Gothic elements in the works of Classical writers such as Aeschylus, Euripides, Ovid, Virgil and Lucan; and his works during this period show clearly that he is also strongly influenced by the irrational, otherworldly qualities present in the philosophies of Plotinus, Plato, and ultimately of Socrates. It is Shelley's philosophical scepticism, with its inherently questioning views of both transcendentalism and rational materialism, which enables him to assume with credibility the role of one who desires to bring his readers into the proximity of the numinous; and as he has rejected all the traditional terminology, imagery and symbolism of Christianity, his use of the Gothic is an essential factor in the realising of his intentions. Even so, it becomes evident that any success in the evocation of the numinous is no more dependent on the writer's openness to the possibility of a non-material future existence, than it is guaranteed by the presence of strongly Gothic qualities in the writing. For instance, any sense of the numinous is virtually absent from Shelley's supernatural last testament, The Triumph of Life, as it is also from The Cenci, which is the most consistently Gothic of all his later poetical works. Nevertheless, my thesis clearly demonstrates that in Prometheus Unbound and Adonais at least, Shelley is, through his use of the Gothic, entirely successful in bringing his readers into the presence of the numinous.