Titus Justus (Titou Ioustou). So Aleph E Vulgate, while B has Titiau Ioustou, while most MSS. have only Ioustou. Evidently a Roman citizen and not Titus, brother of Luke, of Gal 2:1. We had Barsabbas Justus (Act 1:23) and Paul speaks of Jesus Justus (Corinthians Gal 4:11). The Titii were a famous family of potters in Corinth. This Roman was a God-fearer whose house “joined hard to the synagogue” (ēn sunomorousa tēi sunagōgēi). Periphrastic imperfect active of sunomoreō, a late (Byzantine) word, here only in the N.T., followed by the associative instrumental case, from sunomoros (sun, homoros from homos, joint, and horos, boundary) having joint boundaries, right next to. Whether Paul chose this location for his work because it was next to the synagogue, we do not know, but it caught the attendants at the synagogue worship. In Ephesus when Paul had to leave the synagogue he went to the school house of Tyrannus (Act 19:9.). The lines are being drawn between the Christians and the Jews, drawn by the Jews themselves.