They'd arranged for 3 tons of Denfind stone, plus copes plus slabs for the seat area, to be delivered, and had cleared and levelled the chosen spot for us (they also provided us with tea, coffee and hot chocolate and a big box of Quality Street, the lovely people).
* Well, dry-ish. Because it's in a public space, and because people will be sitting on it (and most likely, children will be climbing on it) we discretely mortared anything that wasn't built in beyond any chance of coming out again.