10. Main nave
The nave is 53 metres in length and 15 metres wide with side chapels on either side. These chapels were assigned to the various langues according to seniority. The French, Italian and Aragonese langues being predominant were placed closest to the altar. The entire floor is covered with marble tombstones, beneath which, some of the most illustrious Knights of the Order are laid to rest.
The Grand Masters, who all took great pride in their conventual church, wanted it to be decorated according to the new artistic baroque style. During the 1650s and throughout the 1660s a vast programme of decoration was set into motion. Significant works of art were introduced, for which no expense was spared. Several coats of arms belonging to the aristocratic members of the Order of St John can be seen specifying their contributions.
After the vault decoration the most significant change that transformed the church into a symphony of Baroque splendour was the carving into the soft Maltese stone of the interior walls. On designs prepared by Preti the plain walls of the nave and chapels were decorated with elaborate motifs characteristic of baroque ornamentation, transforming the walls into a riot of richly gilded foliage, flowers, angels and triumphal symbols of all kinds. The pilasters supporting the central nave where clad with the finest green marble and at the top the coat of arms of Grand Master Nicholas Cotoner are displayed.