Further evidence of Christian practices and beliefs during the period of Roman persecution can be found in the many catacombs that lie beneath various parts of Malta, including St Paul's Catacombs and St Agatha's Catacombs in Rabat, just outside the walls of Mdina. The latter, in particular, were beautifully frescoed between 1200 and 1480; they were defaced by marauding Turks in the 1550s. There are also a number of cave churches, including the grotto at Mellieħa, which is a Shrine of the Nativity of Our Lady where, according to legend, St. Luke painted a picture of the Madonna. It has been a place of pilgrimage since medieval times.