Lewis & Short

Sittĭus, a, the name of a Roman gens, e. g. P Sittius, a friend of Cicero, Cic. Sull. 56; Sall. C. 21, 3; Auct. B. Afr. 25; 30. To him is addressed the letter, Cic. Fam. 5, 17; cf. id. ib. 15, 17, 1.
Hence, Sittĭānus, a, um, adj., of Sittius: syngrapha, Cic. Fam. 8, 2, 2; 8, 4, 5: negotium, id. ib. 8, 11, 4.
After him was named Sittianorum colonia = Cirta, Mel. 1, 6, 1; Plin. 5, 2, 3, § 22.