I recently found out that you can block out wide swathes of land easily to deny the AI any ability to settle near you or to protect important areas for future expansion. The AI's settlers must always be accompanied by a military unit. They move in lockstep and will never allow themselves to be isolated. And since the AI cannot enter your borders, nor can military units stack... This means a perfectly valid strategy on the harder difficulties is to simply align your military units side by side with your cities' borders to block off entire areas, potentially half of a continent tip, or to leave a big enough gap, block it off and watch the AI waste resources building settlers trying to get there. This is especially easy if there are some mountains nearby, lakes or any terrain that cannot be properly traversed on. And if necessary, you only need to spend a bit of gold on blocking off coastal tiles. But there's usually no need for that since it's much easier to block off land/coastal access. Also, the AI initially settles in a fixed and observable pattern until it is disrupted by something it can't get to, then it starts looking somewhere else with enough land to settle. If you break the pattern with a city, the AI won't settle behind your cities so it makes it even easily to block off wide areas. I am wondering but does anyone else consistently do this too? You probably can guess which Civilisation can do this 10 times easier, and can even block off huge landmass chunks (and even wall the AI in) with only 3 cities.