In November 1826, the Aniene river flooded and nearly destroyed Tivoli, sweeping away buildings along the old riverbed. Pope Gregory XVI's engineers answered by boring two tunnels through Monte Catillo to reroute the water entirely, completing the diversion by 1835, and let the abandoned gorge become a park instead.
The diverted river now drops roughly 120 meters as the Grande Cascata, one of Europe's tallest artificial waterfalls, into a ravine planted with romantic-era paths. Walkways switchback down past the Neptune and Sirens grottoes to the valley floor, then climb back up to the Acropolis, where the round Temple of Vesta and the rectangular Temple of the Sibyl, both from the Republican era, look out over the gorge that Grand Tour artists came here to paint. FAI reopened the whole park to visitors in 2005 after a major landscape restoration.
