The first member of the gens to achieve prominence was Gaius Ummidius Durmius Quadratus, governor of Syria during the reigns of Claudius and Nero.
The Ummidii held several consulships in the second century, and through the marriage of Gaius Ummidius Quadratus Annianus Verus they were related to the emperor Marcus Aurelius.
The name is mentioned by the poet Horace, where again different manuscripts give it variously, but it appears that the original reading was Ummidius.
[1][3] The family probably came from the town of Casinum, in Latium adiectum, where an inscription mentions Ummidia Quadratilla, who funded the building of an amphitheater and a temple for the townspeople.
In this case, the Ummidii may have been of Volscian origin, although the antiquarian Varro believed the inhabitants of Casinum to be Samnite.