Salzburg is the fourth-largest city in Austria. In 2020, it had a population of 156,852. The town occupies the site of the Roman settlement of Iuvavum. Founded as an episcopal see in 696, it became a seat of the archbishop in 798. Its main sources of income were salt extraction, trade, as well as gold mining. The fortress of Hohensalzburg, one of the largest medieval fortresses in Europe, dates from the 11th century. In the 17th century, Salzburg became a center of the Counter-Reformation, with monasteries and numerous Baroque churches built.