The "Epistles" may be considered among Horace's most innovative works. There was nothing like it in Greek or Roman literature. Occasionally poems had had some resemblance to letters, including an elegiac poem from Solon to Mimnermus and some lyrical poems from Pindar to Hieron of Syracuse. Lucilius had composed a satire in the form of a letter, and some epistolary poems were composed by Catullus and Propertius. But nobody before Horace had ever composed an entire collection of verse letters, let alone letters with a focus on philosophical problems. The sophisticated and flexible style that he had developed in his "Satires" was adapted to the more serious needs of this new genre. Such refinement of style was not unusual for Horace. His craftsmanship as a wordsmith is apparent even in his earliest attempts at this or that kind of poetry, but his handling of each genre tended to improve over time as he adapted it to his own needs. Thus for example it is generally agreed that his second book of "Satires", where human folly is revealed through dialogue between characters, is superior to the first, where he propounds his ethics in monologues. Nevertheless, the first book includes some of his most popular poems.