Originally built sometime before the 4th century, this is certainly one of the oldest churches in the city, and one of the grandest, too. With a nave framed by a processional of two rows of gigantic columns taken from ancient Roman temples and an altar studded with gilded mosaics, this is an interior that often produces involuntary gasps from unsuspecting visitors. Although there are larger naves in Rome, none seems so majestic, as it's bathed in a mellow glow from the 12th- and 13th-century mosaics and overhead gilding. Supposedly the first church in Rome to have been dedicated to the Virgin Mary, the church was rebuilt in the 12th century, and the portico, which was added in the 19th century, seems to focus attention on the 800-year-old mosaics on the facade, which represent the parable of the Wise and Foolish Virgins. The piazza is enhanced by their aura, especially at night, when the front of the church and its bell tower are illuminated. In the interior's mosaics, look for the representation of the Life of the Virgin and note the little building labeled "Taberna Meritoria" just under the figure of the Virgin in the Nativity scene, with a stream of oil flowing from it. It recalls the legend that on the day Christ was born, a stream of pure oil flowed from the earth on the site of the piazza, signifying the coming of the grace of God. Off the north side of the piazza, there's a little street called Via delle Fonte dell'Olio in honor of this miracle.