Ummidia Quadratilla, was a wealthy Roman woman and was a member of the gens Ummidia. She died in the reign of Emperor Trajan (98-117) within a little of eighty years of age, leaving two-thirds (ex besse) of her fortune to her grandson and the other third to her granddaughter (Pliny the Younger Ep. vii. 24). Her grandson Ummidius Quadratus was an intimate friend of Roman Senator and historian Pliny the Younger, who praises her for fostering Quadratus' studies while keeping him untouched by her own luxurious lifestyle.
Quadratilla was probably a sister of Gaius Ummidius Durmius Quadratus, the governor of Syria, who died in 60, and appears to be the same as the Quadratilla mentioned in the following inscription, discovered at Casinum in Lazio: "Ummidia CF Quadratilla amphiheatrum et templum Casinatibus sua pecunia fecit" (Orelli, Inscr. No. 781). It seems that the Ummidii came originally from Casinum.