The Rektoratskirche St. Karl Borromäus, commonly called the Karlskirche (St. Charles Church), is a baroque church located on the south side of Karlsplatz in Vienna, Austria. Widely considered the most outstanding baroque church in Vienna, as well as one of the city's greatest buildings, the church is dedicated to Saint Charles Borromeo, one of the great counter-reformers of the sixteenth century.
In 1713, one year after the last great plague epidemic, Charles VI, Holy Roman Emperor, pledged to build a church for his namesake patron saint, Charles Borromeo, who was revered as a healer for plague sufferers. An architectural competition was announced, in which Johann Bernhard Fischer von Erlach prevailed over, among others, Ferdinando Galli-Bibiena and Johann Lukas von Hildebrandt. Construction began in 1716 under the supervision of Anton Erhard Martinelli. After J.B. Fischer's death in 1723, his son, Joseph Emanuel Fischer von Erlach, completed the construction in 1737 using partially altered plans. The church originally possessed a direct line of sight to the Hofburg and was also, until 1918, the imperial patron parish church.