The altarpiece of the Martyrdom of St Catherine was executed in Naples in 1659 and donated by the artist Mattia Preti to the Italian knights to demonstrate his talent, and as such is one of the first works by the great painter in Malta.
The Italian knights commissioned Preti to design the painting of the vault of St Catherine's although the work was executed by another artist.
One of the most important dates in the year of the Langue of Italy was the Feast Day of St Catherine, 25th November.On the eve of the feast the Grand Master and the Knights Grand Cross assembled in the church of St Catherine where they assisted at the First Vespers chanted by the Conventual Chaplains of the Langue of Italy.
On the Feast itself, at 8 in the morning, the Grand Master and the Knights Grand Cross a assembled once more at the Church of St Catherine for a High Mass. At the same time a high Mass was celebrated in the Chapel of St Catherine in the Conventual church of St John. Then a procession was formed under the direction of the Vice-Prior to carry the Order's most precious relic, the hand of St John the Baptist through the main doors of St John's, down Zachary Street to St Catherine's.
When the relic arrived at St Catherine's the Antiphon of the Benedictus was intoned before the procession then made its way back to St John's, accompanied now by the Grand Master and the Knights Grand Cross holding lighted torches.