I'm enclosing a terrace with a low (2') parapet wall and I was
thinking of making the wall hollow, filling it with soil, and planting
grapes to train along a trellis system that would rise from the wall. 
However I couldn't find anything like this on the net, which makes me
suspect there may be technical reasons not to do this.  Perhaps the
weight of water-laden soil (which I think would need to span about a
foot), would require super-strong or ungainly thick walls on either
side?  Any help would be appreciated.