The great German philologist Richard Heinze's Virgils Epische Technik was originally published in German in 1903. It was the outstanding book on Virgil in its day, and it remains a very valuable study of the techniques Virgil used to compose the Aeneid. This English translation by Hazel Harvey, David Harvey and Fred Robertson was published in 1994, with an introduction by Antonie Wlosok.
"This was the outstanding book on Virgil in its day, and it remains a superlative and basic study of the techniques by which the poet composes his epic on Aeneas.... Heinze's scholarship is absolutely brilliant, even after 90 years." -- W.S. Anderson, author of Essays on Roman Satire