On the surface, the poem describes Dante's travels through Hell, Purgatory, and Paradise or Heaven; but at a deeper level, it represents, allegorically, the soul's journey towards God. At this deeper level, Dante draws on medieval Christian theology and philosophy, especially Thomistic philosophy and the Summa Theologica of Thomas Aquinas. Consequently, the Divine Comedy has been called "the Summa in verse". The work was originally simply titled Comedìa and the word Divina was added by Giovanni Boccaccio. The first printed edition to add the word divina to the title was that of the Venetian humanist Lodovico Dolce, published in 1555 by Gabriele Giolito de' Ferrari.