Ruina montium is Latin for "mountain ruin". Imagine you are playing with a big pile of blocks and you stack them really high to make a tower. But then you accidentally knock it over and all the blocks fall down and become a big mess. That's kind of like what happens with ruina montium, but on a much bigger scale with real mountains.
When people talk about ruina montium, they are usually referring to the damage that happens to mountains because of human activities like mining, logging, or construction. Mountains are really important because they are often home to lots of different animals and plants, and they help keep our air and water clean. But when people come along and dig big holes in them or chop down all the trees, it can really mess things up.
So when we talk about preventing or fixing ruina montium, what we mean is finding ways to keep mountains healthy and safe so that they can keep providing us with all the things we need. This might mean using less resources, finding new ways to do things that don't damage the environment, or coming up with special plans to protect certain areas of the mountains that are especially important. By taking good care of our mountains, we can make sure they stay strong and beautiful for a long time to come!