It is typical for commentators to choose The Tower of 1928 as the collection containing Yeats' mature works. Thirty poems are included in the collection, some of which were previously published in Seven Poems and a Fragment (1922), The Cat and the Moon (1924), and October Blast (1925). (1927). The order in which they appear in The Tower is roughly chronological, with the exception of the last three poems, which do not follow on from the others but which some consider to be among Yeats's best work. Many of these poems are about poets and poetry, making The Tower a valuable resource for students of literature and art history. It is also one of the most challenging poems in the language, so those who struggle with more difficult poems may find it helpful to compare The Tower with other famous poetic sequences such as Milton's Paradise Lost or Byron's Childe Harold's Pilgrimage. Some academics believe that The Tower is an important early example of what later became known as the metaphysical poem. They point out that many of its themes – such as ambition, infinity, and time – would become central to future developments in this kind of writing. Others see it as merely innovative in style rather than content. They note that many of the poems in The Tower use images and concepts that had been popular with modernists like Eliot and Pound, while others resemble traditional Irish poetry in their use of meter and rhyme scheme.