St. Johns Co-Cathedral, located in Valetta, Malta, was built between 1573 and 1578. It was designed by the Maltese military architect Gerolamo Cassar who has designed several of the more prominent buildings in Valetta. The inside was largly designed by Mattia Preti , the Calabrian artist and Knight. Preti designed the intricate carved stone walls and painted the vaulted ceiling and side altars with scenes from the life of St John.

St. Johns was originally the regular church of the Hospitalers (the Knights of Saint John) but grew to equal prominence with the archbishop's cathedral at Mdina.

St. Johns is also the home of a small art collection by the famous painter Caravaggio (1571-1610), one of his most famous paintings "Beheading of Saint John the Baptist" (1608) can be found here as well as "Jerome III" (1607-1608). You can also see a number of replicas of his paintings here.