The basilica is also known as Our Lady of the Snow, in honor of the miracle that brought about this beautiful church in A.D. 435.
During the pontificate of Liberius, the Roman patrician John and his wife, who were without heirs, made a vow to donate their possessions to the Virgin Mary. They prayed that she might make known to them how they were to dispose of their property in her honour. On 5 August, at the height of the Roman summer, snow fell during the night on the summit of the Esquiline Hill. In obedience to a vision of the Virgin Mary which they had the same night, the couple built a basilica in honour of Mary on the very spot which was covered with snow.
Click on a link to the Vatican website beginning a virtual tour.