If you have the gold to finish a wall in two of your cities without walls in turn 60, and a warrior + catapult everywhere, the first barbarians have no chance. Alternatively in cities with a warrior + wall you need the gold to finish the catapult in one or two cities under attack.
As others wrote in another thread, wall+phalanx+phalanx should be also good enough. And it doesn't need to be ready everywhere, you only must have the gold to get it ready immediately if a city is under attack. They are attracted by weak cities, no wall, not populated, not your capital. and you are in trouble. If your cities are good they attack the weak AIs
Disabling barbarians is too
easy, you (and the AIs) can get a boost in turn 1 if you set dispersion=1 instead of the default dispersion=0. With that your initial units end up on 3x3 tiles instead of 1x1, you might immediately see a good tile for your first city, and after 60 turns this initial boost is a huge advantage against any barbarian trying to visit you. Kill the barbarian leader (on land) for a ransom of 100 gold, and they end up to pay for your expensive walls.