A large green space in the historic centre of Cagliari is home to thousands of plant species from all over the world, some of them very rare, and at its core is an archaeological area that houses a large number of Roman remains. The Botanical Gardens are shaped like a trapezoid and cover an area of about five hectares at the lower end of the Palabenda valley, in an area that includes the Anfiteatro romano, Orto dei cappuccini vegetable garden and villa di Tigellio, where there are other Roman domus remains and what was once a thermal baths. The idea of creating a botanical garden in the valley came about in 1820. It had once belonged to the Jesuits, then to the ruling family, to a series of private individuals and was then purchased by the university. Work on the project began in 1864 under the guidance of the founder Patrizio Gennari, who modified the original project designed by the architect Gaetano Cima.