Thaumastus was a friend and uncle of Sidonius Apollinaris

Sidonius Apollinaris

Gaius Sollius Apollinaris Sidonius or Saint Sidonius Apollinaris was a poet, diplomat, and bishop. Sidonius is "the single most important surviving author from fifth-century Gaul" according to Eric Goldberg...

. His brother, the elder Apollinaris was born around 405 and was the praetorian prefect of Gaul under Valentinian III

Valentinian III

-Family:Valentinian was born in the western capital of Ravenna, the only son of Galla Placidia and Flavius Constantius. The former was the younger half-sister of the western emperor Honorius, and the latter was at the time Patrician and the power behind the throne....

 between 425 and 455. Thaumastus and his brother were both sons of another Apollinaris, praetorian prefect of Gaul before 409 and were friends with his successor Decimus Rusticus

Decimus Rusticus

Decimus Rusticus of Treves and Lyon he was a Master of the Offices and the praetorian prefect of Gaul between 409 and 410 or 413. He was one of those responsible for the withdrawal from Britannia...

. Thaumastus was associated with Tonantius Ferreolus

Tonantius Ferreolus (prefect)

Tonantius Ferreolus was the praetorian prefect of Gaul from 451.He was either "personally related to" or "connected through relatives" with Sidonius Apollinaris, and was associated with Thaumastus in the impeachment of Arvandus...

 in the impeachment of Arvandus

Arvandus

Arvandus was a Gaul who rose through the hierarchy of Imperial Roman society to twice be appointed Praetorian prefect of Gaul.On the first occasion, 461, he was appointed by Emperor Libius Severus. This appointment ended when Severus died in 465...

. He was the father of Eulalia, born in 425 and married before 450 to Flavius Probus

Flavius Probus

Flavius Probus , a Roman Senator and a v. nob. of Narbonne, then Narbo, was a man of literary taste and precocious ability. His father was Flavius Magnus, Consul of Rome in 460...

, Roman Senator.

He seems to be a descendant of another Apollinaris, praetorian prefect of Gaul under Constantine II

Constantine II (emperor)

Constantine II , was Roman Emperor from 337 to 340. Co-emperor alongside his brothers, his short reign saw the beginnings of conflict emerge between the sons of Constantine the Great, and his attempt to exert his perceived rights of primogeniture ended up causing his death in a failed invasion of...

between 337 and 340.