Deuteronomy 3:4
And we took all his cities at that time, there was not a city which we took not from them, threescore cities, all the region of Argob, the kingdom of Og in Bashan. And we took all his cities at that time, there was not a city which we took not from them, threescore cities, all the region of Argob, the kingdom of Og in Bashan.
The verse records Israel's complete taking of Og's kingdom, all sixty cities of the region of Argob in Bashan, with not one city left untaken. Those cities were fortified cities built of stone with formidable defenses. They belonged to a powerful and populous kingdom, and besides the sixty there were surrounding unwalled towns, and their size and defenses made them appear impossible to conquer with the forces then available. The conquest was accomplished through God's deliverance rather than by Israel's military strength.
The overthrow of Og's power and kingdom took place before Israel crossed the Jordan. Together with the crossing of the swollen Jordan, that defeat showed Israel and the surrounding nations that God was with His people and filled those nations with fear.