The Book of Hours was a collection of prayers and devotions that became very popular during the late Middle Ages and Renaissance for lay worship. Because his edition omits much of the usual text, Aldus's purpose may have been to provide a Greek text for pedagogical purposes to students who would have been intimately familiar with the Latin version. Or perhaps he did it as a favor to his Uniate Catholic friends, members of the Greek Orthodox church who favored union with Rome. These might have appreciated a printed edition of the Greek version of an important text of the Roman rite. The size of the Horae Beatissimae Virginis, typical for printed prayer books, anticipates the introduction of the octavo format in 1501, and may have suggested it to Aldus.