Nerva–Antonine dynasty
Bassus was born in a senatorial family, the son of Lucius Septimius Severus (b. c. 245) and his wife, Pomponia Bassa (born c. 250). His paternal grandfather was Lucius Septimius (b. c. 210), while his maternal grandparents were the Roman Senator Pomponius Bassus and the noblewoman Pomponia Gratidia. Through his maternal grandfather, Bassus was a descendant of the Roman emperor Marcus Aurelius, Roman empress Faustina the Younger and of the former ruling Nerva–Antonine dynasty of the Roman Empire.