I think about this too, a lot. In two, maybe three generations, our deaths will be forgotten. Everything we've built, people we've touched, love gained and lost, will be gone. Who will remember us? Perhaps someone doing research for a family tree will stumble on our names in some dusty archive.
Everything will crumble away, just like those monuments. They're reminders of what was. The only thing I've found that can slow time is a photograph. My Aunt has a photo-book of her grandparents from E. Prussia from the 1800's. I can look and see what it was like back then. I can see my maternal grandmother as a child. My Aunt's book is starting to crumble, the photographs are turning brown.
While thinking this way is melancholic - I'm very much in this state now myself - it can be liberating. Live your life with "balls to the wall", take no prisoners, and with "fuck no regrets," because it all will fade away one time.
We will be dead longer than we were alive. xoxoxo