Granito del foro is a distinctive igneous rock, in fact a granodiorite rather than a granite, long known and named for its use in buildings of the Roman Forum. Exactly what is it? Where does it come from? Where else was it used and not used? What does the granito del foro say about ownership and empire?
Peacock, D. P. S.; Williams-Thorpe, Olwen ; Thorpe, R. S. and Tindle, A. G. (1994). Mons Claudianus and the problem of the 'granito del foro': a geological and geochemical approach. Antiquity, 68(259) pp. 209–230.