 Swamps are the breeding ground of Anopheles mosquitoes, the vectors of malaria which had been plaguing Sardinia since the Phoencian first arrived, until the swamps were drained and treated with DDT in the 20th century.During the siege of Cagliari, the Aragonese built a sanctuary to the Virgin Mary on top of the hill.In 1335, King Alfonso the Gentle donated the church to the Mercedarians, who built an abbey that stands to this day.