In 1805–1814 it became briefly part of the Napoleonic Kingdom of Italy, a client-state of the French Empire. After the 1815 Congress of Vienna, Ferrara was given back to the Pope, now guaranteed by the Empire of Austria. A bastion fort erected in the 1600s by Pope Paul V on the site of and old castle called "Castel Tedaldo", at the south-west angle of the town, was thus occupied by an Austrian garrison from 1832 until 1859. All of the fortress was dismantled following the birth of the Kingdom of Italy and the bricks used for new constructions all over the town. During the last decades of the 1800s and the early 1900s, Ferrara remained a modest trade centre for its large rural hinterland that relied on commercial crops such as sugar beet and industrial hemp. Large land reclamation works were carried out for decades with the aim to expand the available arable land and eradicate malaria from the wetlands along the Po delta. Mass industrialisation came to Ferrara only at the end of the 1930s with the set-up of a chemical plant by the Fascist regime that should have supplied the regime with synthetic rubber. During the Second World War Ferrara was repeatedly bombed by Allied warplanes that targeted and destroyed railway links and industrial facilities. After the war, the industrial area in Pontelagoscuro was expanded to become a giant petrochemical compound operated by Montecatini and other companies, that at its peak employed 7,000 workers and produced 20% of plastics in Italy. In recent decades, as part of a general trend in Italy and Europe, Ferrara has come to rely more on tertiary and tourism, while the heavy industry, still present in the town, has been largely phased out. After almost 450 years, another earthquake struck Ferrara in May 2012 causing only limited damage to the historic buildings of the town and no victims. The town of Ferrara lies on the southern shores of the Po river, about 44 km (27 mi.) north-east of the regional capital, Bologna, and 87 km (54 mi.) south of Venice. The territory of the municipality, entirely part of the Padan plain, is overwhelmingly flat, situated on average just 9 metres (30 ft.) above sea-level. The proximity to the largest Italian river has been a constant concern in the history of Ferrara, that has been affected by recurrent, disastrous floods, the latest occurring as recently as 1951. The Idrovia Ferrarese links the river Po from Ferrara to the Adriatic at Porto Garibaldi.