κατ' ἰσχύν

From LSJ

Οὗτος Ἰουστῖνον καὶ Νεοβιγάστην στρατηγοὺς προβαλόμενος, καὶ τὰς Βρεττανίας ἐάσας, περαιοῦται ἅμα τῶν αὐτοῦ ἐπὶ Βονωνίαν → He appointed Justinus and Neovigastes as generals, and leaving Britain, crossed with his forces to Bononia.(Olympiodorus/Photius)

Source

Greek > English (Woodhouse)

by force, by violence