The gens Didia, or Deidia, as the name is spelled on coins, was a plebeian family at ancient Rome, which first appears in history during the final century of the Republic. According to Cicero, they were novi homines. Titus Didius obtained the consulship in 98 BC, a dignity shared by no other Didii until imperial times.

Origin

The nomen Didius or Deidius is of uncertain origin. It resembles a class of gentilicia formed from cognomina ending in -idus, but might be derived from a cognomen Dida. Chase classifies it among those gentilicia that either originated at Rome, or cannot be shown to have come from anywhere else. Anthony Birley suggests they came from eastern Italy, "specifically from the coastal town of Histonium." Olli Salomies has documented several examples of Diidiis used as a family name amongst the Oscans.

Praenomina

The earlier Didii used the praenomina Sextus, Titus, and Gaius, to which later members of the family added Quintus, Aulus, and Lucius. All of these were common throughout Roman history.

Branches and cognomina

None of the Didii mentioned during the Republic is known to have borne a cognomen. A number of surnames are found under the Empire, of which the only one that appears to be a family name is Gallus. This cognomen, referring to a cockerel, belongs to an abundant class of cognomina derived from the names of everyday objects and animals. The same surname could also refer to a Gaul, indicating someone of Gaulish descent, or whose appearance or character resembled that of a Gaul.

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