Dionysius of Halicarnassus was a Greek historian, rhetorician, and literary critic who lived and worked in Rome during the late 1st century BCE. He arrived around 30 BCE and spent over two decades there, teaching rhetoric and researching Roman history. His position allowed him to act as a cultural intermediary, interpreting Roman history for a Greek audience while teaching Greek rhetorical arts to the Roman elite.

His most significant work is the Roman Antiquities, a 20-book history of Rome from its origins to 264 BCE, of which roughly half survives. His critical treatises, including On the Ancient Orators, On Thucydides, and On the Arrangement of Words, exemplify his commitment to Attic style and provide foundational analysis of classical oratory and historiography.

Dionysius is a crucial primary source for early Roman history, offering a detailed, pro-Roman narrative aimed at reconciling Greek audiences to Roman rule. As a leading proponent of Atticism, his literary criticism established influential principles of rhetorical theory and style.