I was feeling a little winter tired when I read this, and I immediately recalled two wonderful memories of Rome, even had these photos from my last visit to Rome, in 2003 (so long ago!) ... one at the Forum and another in the Vatican Museums, both of which seem to fit Ross' description of moss and fern covered ruins.
First the Forum, which was actually full of fascinating vegetation in early May ...
At the entrance to the Palatine Hill is this striking composition of ferns, mosses, a few callas, and I don't know what else, water seeping continually down through the mass of vegetation on rock. Is this a vertical garden from antiquity? I've always wondered whether this was created in more recent times, or perhaps started as a spring, its beauty recognized and "cultivated" over the centuries. It's quite large, maybe twenty or so feet tall, as I remember.
Whatever it is, it captured my fancy when I first saw it many years ago, long before I became a gardener, and has remained as a powerful visual memory. If you know anything about this "vegetable fountain," please let me know.
So this is how I interpret Ross' suggestion for my Brooklyn garden. Crazy, I suppose. So very out of place to my mind. Even if something like this could be created in our climate, would it ever seem right? But what a wonderful fantasy!