The roof of the edifice, which is divided into zones, is superbly painted in elaborate designs, representing hundreds of figures of such proportions as to appear from the floor to be of life-size. The subjects are mainly Scriptural themes, especially relating to the life of St. John, painted in oil laid on the stone, which the artist prepared by a peculiar process devised for this purpose. At the corners of each of the arches are a score of figures representing martyrs and heroes, illustrative of the history of the knightly order. The real genius displayed in the designs could only be born of one inspired by a true love of art, together with a devoutly religious spirit. The excellence of the designs and the naturalness of the army of figures challenge both surprise and admiration. They are so artistically done that it is difficult not to believe them to be in bas-relief. The whole was the patient work of one prolific artist, Mattia Preti, an accomplished and enthusiastic Calabrian, who spent forty years of his life in the special adornment of the church of St. John, refusing, it is said, all pecuniary remuneration for the same. He was quite content to live frugally, exercising strict self-denial, that he might thus exemplify his art and his religious devotion. Preti studied the rudiments of his chosen calling with his brother, who was director of the Academy of St. Luke, at Rome, and brought with him to Malta not only ability and experience, but a devout love of art for art's sake. His body lies buried before the entrance to the vestry, the artist having died in 1739, well advanced in years, and leaving behind him, in Malta, a vast number of examples of his ability, which form an appropriate monument to his memory. As evidence of his indefatigable industry, it should be mentioned that in the cathedral of Città Vecchia in the centre of the island, other specimens of Mattia Preti's work in the same line of church adornment may be seen, together with some fine individual pieces of composition.