Gaius Ummidius Quadratus Sertorius Severus was a Roman senator active during the second century AD.
Syme infers from the last two elements in his name that either Quadratus' father, or his mother's brother was one Sertorius Severus, and identifies him with a correspondent of Pliny the Younger.
Anthony Birley identifies Quadratus' mother with an aunt of Marcus Aurelius, "a fourth child of old Annius Verus and Rupilia Faustina".
[6] In a letter to his friend Geminus dated to the year 107, Pliny writes of the death of Quadratus' grandmother just shy of her eightieth birthday.
[9] The Historia Augusta mentions Quadratus in a list of three men—the other two being Lucius Catilius Severus and Marcius Turbo—whom the emperor Hadrian treated harshly.