By the general consent of critics the first praise of genius is due to the writer of an epic poem, as it requires an assemblage of all the powers which are singly sufficient for other compositions. Poetry is the art of uniting pleasure with truth, by calling imagination to the help of reason. Epic poetry undertakes to teach the most important truths by the most pleasing precepts, and therefore relates some great event in the most affecting manner.[Samuel Johnson, Life of Milton.]
The Fortnightly Books are Paradise Lost and Paradise Regained, by John Milton. Paradise Lost was originally published in 1667, although the revised form was published in 1674. Paradise Regained, Milton's 'small epic', was published in the middle in 1671. Milton was almost sixty when the first edition of Paradise Lost came out, having been blind for fifteen years, and the poems had to be done by dictation to anyone who was available and could write it down.
Of Paradise Lost, perhaps no introduction is particularly needed; in it Milton set out to create an epic poem in blank verse. His original idea seems to have been to build an Arthurian epic, but this seems to have been quickly replaced by the idea of an allegorical work on the topic of the Fall, perhaps inspired by mystery plays, which was reworked until it became the poem we have.
According to a famous anecdote by the Quaker Thomas Ellwood, Ellwood remarked to Milton, "Thou hast said much here of Paradise lost, but what hast thou to say of Paradise found?" Milton changed the subject, but later shared the manuscript of Paradise Regained with him. There's evidence, though, that Milton had already been working on the poem. It considers the reversal of the events of Paradise Lost, of course, but unexpectedly takes the Temptation in the Wilderness rather than the Passion as its subject matter.
Somewhere around here I have C. S. Lewis's A Preface to Paradise Lost, and will have to re-read that, as well. Penderecki has a famous opera based on Paradise Lost that I might look into if I have the time.