[5] Following the Great Siege of 1565, St. John's Co-Cathedral was commissioned in 1572 by Jean de la Cassière, Grand Master of the Order of St.

[7] Construction of the oratory and sacristy began in 1598, during the magistracy of Martin Garzez, and they were completed by Grand Master Alof de Wignacourt in 1604.

[12] The annexes on the side of the cathedral were added later and feature the coat of arms of Grand Master António Manoel de Vilhena who reigned from 1722 to 1736.

"[13] In the mid-19th century, Giuseppe Hyzler, a leader of the Nazarene movement, removed some of the Baroque art of the cathedral, including the ornate altar in the Chapel of the Langue of France.

[14] The cathedral's exterior was slightly damaged by aerial bombardment in 1941, during World War II, barely escaping total destruction.

[16] Today, the cathedral is one of the most popular tourist attractions in Malta,[12] and is listed on the National Inventory of the Cultural Property of the Maltese Islands.

[5] The doorway is flanked by Doric columns supporting an open balcony from which the Grand Master used to address the people on important occasions.

[19][18] Overall, the exterior is rather austere and reminiscent of a fortress,[20] reflecting both Cassar's style as a military engineer as well as the Order's mood in the years following the Great Siege of Malta in 1565.

Preti designed the intricate carved stone walls and painted the vaulted ceiling and side altars with scenes from the life of John the Baptist.

[22] The funerary monument of Grand Master Marc'Antonio Zondadari (died 1722), nephew of Pope Alexander VII, is located close to the main entrance.

Restored in the late 1990s in Florence, this painting is one of Caravaggio's most impressive uses of the chiaroscuro style for which he is most famous with a circle of light illuminating the scene of St John's beheading at the request of Salome.

Among the contents of the museum there are the Flemish Tapestries designed by Peter Paul Rubens, which were donated by Grand Master Ramon Perellos y Roccaful,[38][39] paintings of Grand Masters Jean de la Cassière, Nicolas Cotoner and Manuel Pinto da Fonseca, and paintings which were formerly in the side chapels such as St. George killing the Dragon by Francesco Potenzano.

[41] This fee includes the provision of audio guides available in Maltese, English, Italian, French, German, Spanish, Japanese and Russian.