I've always thought of Piranesi as a sculptor; when I look several times a week at the giant, spectacular, if rather ugly "Piranesi vase", which towers above your head in a riot of decorated marble in the Enlightenment gallery in the British Museum, that's perhaps not surprising, but I'm learning from Marguerite Yourcenar that he was primarily, and probably most importantly, an artist and engraver.
He produced "coffee table books" (no they hadn't invented "coffee tables" then, but it describes their nature - something that was a status symbol as well as a beautiful text) - that sold to the same clients as bought his "restored" sculptures. (Sometimes so restored there was only a tiny fraction of ancient material involved.)
Piranesi was very much of the artisan class, although he was ennobled by the Pope in 1767. Yourcenar is interesting on the way in which he did not regard himself as an "artist" in the prima dona-ish way that is often regarded today.
"To the last he docilely follows custom, which consists in numbering on the plates each part of the structure, each fragment of ornament still in place, and making certain explanatory notes in the lower margin corresponding to them, without it ever occurring to him, as it certainly would to an artist nowadays, that these schoolbook specifications or engineering diagrams might diminish the aesthetic or picturesque value of his work." (p. 98)
Yourcenar (writing in the Sixties) notes that about a third of the structures Piranesi recorded did not survive, and many more had been significantly modified or "restored" in unsympathetic ways. His work is thus a hugely valuable record of what has been, only relatively recently, lost.
He did, however, have an "artistic" side, expressed in the curiously modern-feeling Imaginary Prisons (1745). Supposed to have been done while he was suffering from a fever (quite likely malaria), they have a haunting, frightening insanity reminiscent of the late Goya.