Further evidence of Christian practices and beliefs during the period of Roman persecution appears in catacombs that lie beneath various sites around Malta, including St. Paul's Catacombs and St. Agatha's Catacombs in Rabat, just outside the walls of Mdina. The latter, in particular, were frescoed between 1200 and 1480, although invading Turks defaced many of them 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 the medieval period.