Linz is located in northeastern Austria, with a population of approximately 200,000. It is the capital of Upper Austria and the third-largest city in Austria. Linz is situated about 30 kilometres south of the Czech border, and it is also an important river port and economic centre on the upper Danube River, as well as Austria's most important heavy industrial city, housing the country's largest steel and chemical companies. Mozart's residence, Mozarthaus, in early November 1783, Mozart stayed here as a guest of Count Thun. Landstraße forms the main axis of the city; it features many historic buildings and attractions, such as the Ursuline Church (Ursulinenkirche) and the Carmelite Church (Karmeliterkirche), and is the third most visited shopping street in Austria. The Linz City Parish Church (Stadtpfarrkirche) is a late Romanesque complex, with Baroque elements added in 1648. Frederick III died in Linz on 19 August 1493, and the emperor's heart is buried here.