A wall separates R and myself when we sleep, a less than soundproof wall. At least if he is snoring, he is alive. It's when I don't hear him snoring I worry.
There is the very old Great Wall of China, and the more recent Hadrians Wall in England. There was a wall in Berlin, dividing the city between East and West Germany. Walls are to divide things, or to keep people in or out.
Australia doesn't have border walls. We are an island and our borders fiercely protected by our conservative government against refugee boat people. While I am quite open to discussing our refugee intake, I do believe that our island border needs to be secure. We know it is not. Drugs, people, all sorts of things come into Australia via our insecure ocean border. We need to control who and what comes into Australia.
The absolutely appalling President of the US who I hope I see in gaol one day, does have a point about his wall though. It is not unreasonable for the United States to have a secure border at its southern boundary. In fact the effort that is put into policing its northern border with Canada seems like a absolute joke. No cheap workers flooding in from Canada, I suppose, just........what? I don't think those seeking a better life.