When did you start wearing pants?

Gibbon writes (1.XI note 87) about the European pretender-emperor Tetricus, conquered by Aurelian in 274, that he was paraded through Rome in trousers:

"The use of braccae, breeches, or trowsers [sic], was still considered in Italy as a Gallic and Barbarian fashion. The Romans, however, had made great advances towards it.

"To encircle the legs and thighs with fasciae, or bands, was understood in the time of Pompey and Horace to be a proof of ill-health or effeminacy.

"In the age of Trajan, the custom was confined to the rich and luxurious. It gradually was adopted by the meanest of the people. See a very curious note of Casaubon, ad Sueton. in August. c. 82."