St. Johns Co-Cathedral (Maltese: Kon-Katidral ta’ San Ġwann), in Valletta, was built by the Knights of Malta between 1573 and 1578, having been commissioned in 1572 by Grand Master Jean de la Cassière as the conventual church of the Order of the Knights Hospitaller of St John, known as the Knights of Malta.
The Church was designed by the Maltese military architect Glormu Cassar (Girolamo Cassar) who designed several of the more prominent buildings in Valletta. The church is considered to be one of the finest examples of high Baroque architecture in Europe and one of the world's great cathedrals.