Several facilities for supplying this commodity in Roman Italy were built at Subiaco. The Anio Vetus was a poor quality source of this commodity compared to the Anio Novus. After being appointed as a curator named for this commodity, Frontinus wrote a series of treatises about its supply system. This commodity was used in chambers built on top of stacks of pilae tiles. A source of this commodity belonging to the Celtic goddess (*) Sulis gave its name to a Roman (10[1])town. The Pont du Gard near Nîmes, France was built for this (10[1])commodity. A hypocaust heated this (10[1])commodity before use in a caldarium. A city in Somerset, England is named for housing Roman thermae that used this commodity. For 10 points, name this substance that Roman engineers transported with aqueducts. ■END■