When Gallio was proconsul of Achaia (Galliōnos de anthupatou ontos tēs Achaias). Genitive absolute of present participle ontos. Brother of Seneca the Stoic (Nero’s tutor) and uncle of Lucan the author of the Pharsalia. His original name was M. Annaeus Novatus till he was adopted by Gallio the rhetorician. The family was Spanish. Gallio was a man of culture and refinement and may have been chosen proconsul of Achaia for this reason. Statius calls him “dulcis Gallio.” Seneca says of him: Nemo enim mortalium uni tam dulcis quam hic omnibus (No one of mortals is so pleasant to one person as he is to all). Luke alone among writers says that he was proconsul, but Seneca speaks of his being in Achaia where he caught fever, a corroboration of Luke. But now a whitish grey limestone inscription from the Hagios Elias quarries near Delphi (a letter of Claudius to Delphi) has been found which definitely names Gallio as proconsul of Achaia (authupatos tēs Achaias). The province of Achaia after various shifts (first senatorial, then imperial) back and forth with Macedonia, in a.d. 44 Claudius gave back to the Senate with proconsul as the title of the governor. It is amazing how Luke is confirmed whenever a new discovery is made. The discovery of this inscription has thrown light also on the date of Paul’s work in Corinth as it says that Gallio came in the 26th acclamation of Claudius as Emperor in a.d. 51, that would definitely fix the time of Paul in Corinth as a.d. 50 and 51 (or 51 and 52). Deissmann has a full and able discussion of the whole matter in Appendix I to his St. Paul.
Rose up (katepestēsan). Second aorist active of kaṫepḣistēmi, intransitive, to take a stand against, a double compound verb found nowhere else. They took a stand (estēsan) against (kata, down on, epi, upon), they made a dash or rush at Paul as if they would stand it no longer.
Before the judgment seat (epi to bēma). See Act 12:21. The proconsul was sitting in the basilica in the forum or agora. The Jews had probably heard of his reputation for moderation and sought to make an impression as they had on the praetors of Philippi by their rush (sunepestē, Act 16:22). The new proconsul was a good chance also (Act 25:2). So for the second time Paul faces a Roman proconsul (Sergius Paulus, Act 13:7) though under very different circumstances.