1981 [Gerstenberg/Research Press], John W. Welch, Chiasmus In Ancient Greek and Latin Literatures, John W. Welch (editor), Chiasmus in Antiquity, 2020, Wipf and Stock, page 261, In the Aeneid, Vergil uses chiasmus in order to make his poetry smoother and more picturesque. Many lines could be quoted in which a chiastic order of words was necessary to maintain the dactylic hexameter.
Source: wiktionary