Gaius Asinius Quadratus was a Greek historian of the Roman imperial period active in the 3rd century CE. He lived during the reign of Emperor Alexander Severus and likely into the subsequent era. His Roman nomen and the title "clarissimus" indicate he was a senator, reflecting the integration of Greek intellectuals into the Roman elite.

His only known work is A History of Rome in Fifteen Books, also called The Millennium or Chilieteris. This lost history, composed in the archaic Ionic dialect, covered a thousand years from Rome's foundation to the reign of Alexander Severus and survives only in fragments.

Quadratus is significant as a Greek historian writing Roman history for a Greek audience within the Empire. His deliberate use of the Ionic dialect was an archaizing imitation of Herodotus, characteristic of the Second Sophistic movement. His work was used as a source by later Byzantine compilers, and his senatorial rank provides a perspective from within the imperial administration he described.