Greek historian and teacher of rhetoric whose history (historiography) of Rome is, with Livy's, the most valuable source from early Roman history. This work, called Rhōmaïke archaiologia (Roman Antiquities), treats Rome from its origins to the First Punic War. Though clearly written from a pro-Roman standpoint, it was carefully researched.

Dionysius migrated to Rome in 30 BC, and his history, which sought to justify the Romans to the Greeks, began to appear in 7 BC. Of its 20 books, only the first 11 (to 441 BC) survive in complete form. He is believed to have used this work as a practical demonstration of rhetorical principles. Peri mimēseos (On Imitation; in three books) survives in fragments and seems to have influenced the great Roman educator Quintilian. Dionysius's individual essays on the 4th-century-BC Attic orators Lysias, Isocrates, Isaeus, and Demosthenes begin with a praise of Roman writers for turning away from Hellenistic Greek models (Asianism) toward Classical authors (Atticism). He discussed the eminent historian Thucydides in an important essay and in a letter to his friend Ammaeus. His essay "Peri syntheseos onomaton" ( "On the Arrangement of Words" ; often cited by its Latin title, "De compositione verborum" ) is the only extant ancient discussion of word order. Dionysius was a mediocre historian but a first-rate literary critic who examined authors' style and historical context.