How Was Tivoli Built

Villa Adriana is the most ambitious thing here and the least obviously legible, because it is a ruin spread across 120 hectares rather than a building. Its defining idea is separation: an entire network of tunnels and underground roads carried staff, deliveries and carts beneath the site, so that the imperial household moved through gardens apparently staffed by nobody.

Individual structures quote places Hadrian had seen. The Canopus is a long pool with a colonnade and a vaulted dining hall at the end, referring to an Egyptian canal; the Maritime Theatre is a circular island villa inside a moat, reached by a swing bridge, apparently the emperor’s private retreat.

Villa d’Este solves a harder engineering problem than it looks. The site is a steep slope with no water at the top, so a channel was cut for about a kilometre beneath the town to bring the Aniene in above the garden. Everything below runs on the fall of that water: five hundred fountains, the Hundred Fountains along a terrace wall, and the Oval Fountain, with no pump in the system then or now.

The town above is medieval in fabric, built largely of local travertine on Roman foundations, with the Rocca Pia — a four-towered fortress put up by Pope Pius II in 1461 — placed to overawe the inhabitants rather than to defend them.