It is looked upon as certain by the historians of Paris that the Cathedral of Notre Dame stands on the site formerly occupied by a heathen temple. But how and when the transformation took place is not known, though the period is marked more or less precisely by the date of the introduction of Christianity into France. Little confidence, however, is to be placed in those authors who declare that the Paris cathedral was founded in the middle of the third century by St. Denis, the first apostle of Christianity in France; for at the very time when St. Denis was preaching the Gospel to the Parisians the severest edicts were still in force against Christians. It cannot, then, be supposed that the officials of the Roman Empire would have tolerated the erection of a Christian church. It can be shown, however, that under the episcopacy of Bishop Marcellus, about the year 375, there already existed a Christian church in the city of Paris, on the borders of the Seine and on the eastern point of the island, where a Roman temple had formerly stood. Towards the end of the sixth century the cathedral was composed of two edifices, close together, but quite distinct. One of these was dedicated to the Virgin, the other to St. Stephen the Martyr. Gradually, however, the Church of our Lady was extended and developed until it touched and embraced the Church of St. Stephen. The Church of St. Mary, as many called it, was the admiration of its time. Its vaulted roofs were supported by columns of marble, and Venantius Fortunatus, Bishop of Poitiers, declares that this was the first church which received the rays of the sun through glass windows. More than once it is said to have been burnt during the incursions of the Normans. But this is a matter of mere tradition, and the destruction of the cathedral by fire, whether it ever occurred or not, is held in any case to have been only partial. In the twelfth century Notre Dame was, it is true, known as the "New Church." This appellation, however, served only to distinguish it from the smaller Church of St. Stephen (St. Etienne), which had been left in its original state, without addition or renovation.