Some borders stay the same for centuries, some change often due to wars or treaties. I was able to experience a few of them, first hand.
China and Russia (2615 miles)
Though I never crossed into China from Russia, we were told several times, while taking the Trans-Siberian Railway, that China loomed on the horizon. Likewise, for Mongolia. Not a big deal!
Argentina and Chile (3293 miles)
On our long drive down (and up) Chile, we crossed the border several times, by plane, bus, car, and foot. The most interesting was on our trip back into Chile from Ushuaia, Argentina on a 12.5-hour bus ride. Out in the middle of the Patagonian Steppe, we crossed the border. First, the Argentine border patrol processed us, then a few hundred feet down the road, the same for Chile’s border patrol. Out in the middle of nowhere. Only a small convenience store for snacks and water, perhaps a lottery ticket, and some booze.
Kazakhstan and Russia (4254 miles)
I don’t remember much about this, other than a few Kazakhs boarding our train in the middle of the night.
USA and Canada (5525 miles)
People often forget these are the world’s second and fourth largest countries. The border passes 13 U.S. states, and 8 Canadian provinces. It is primarily an east-west border, with four Great Lakes also part of the border. I have crossed this border almost a dozen times. And each time, it gets a little more “bureaucratic”, if you know what I mean. Crossing by auto is, by far, the worst way. They ask many questions, and often inspect your vehicle for guns, drugs, and fruit. A peaceful border until recently!
My most memorable border was much smaller. Crossing the Berlin Wall remains one of the most intimidating and memorable border crossings in my life. The Wall was only 156.4 km, mostly concrete walls, and metal mesh fence, along the death strip. I crossed twice, once on a tour bus, and once on foot. It was an experience of a lifetime!