Quintus was Marcus’ younger brother, born between 105 and 102 B.C. Before November 68 (Att. 1, 5, 2, first extant letter to Atticus, stands as terminus ante quem), he had married Pomponia, sister of Cicero’s lifelong friend T. Pomponius Atticus, who gave him his only son, Quintus junior, in 67; yet their union was notoriously unhappy and quarrelsome, in spite of Cicero’s and Atticus’ soothing efforts (see the domestic row during a lunch party narrated in Att. 5, 1, 3-4, in May 51), so that they eventually divorced at the end of 45 or beginning of 44.
Following on his brother’s tracks, Quintus entered politics under Marcus’ protection and supervision: he was quaestor in some unidentified …
Prost, François. "Quintus Tullius Cicero". The Literary Encyclopedia. First published 14 February 2013
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