The richly decorated campanile (1750 to 1754 , by Vanvitelli, is of great height; the principal bell, presented by Leo X in 1516 , weighs 11 tons. The interior of the church has mosaics by Domenichino and Guido Reni and other works of art, including statues by Raffaello da Montelupo. In the sacristies on each side of the right transept are frescoes, on the right by Melozzo da Forli, on the left by Luca Signorelli. In both are fine intarsias. The basilica as a whole is thus a collaborative masterpiece by generations of architects and artists.
It is a plain stone building, 8.5 m (28 ft) by 3.8 m (12 1/2 ft) and 4.1 m (13 1/2 ft) high; it has a door on the north side and a window on the west; and a niche contains a small black image of the Virgin and Child, in Lebanon cedar, and richly adorned with jewels. The statue was commissioned after a fire in the Casa Santa in 1921, and was crowned in the Vatican in 1922 by Pope Pius XI. Around the house is a tall marble screen designed by Bramante and executed under Popes Leo X, Clement VII and Paul III, by Andrea Sansovino, Girolamo Lombardo, Bandinelli, Guglielmo della Porta and others. The four sides represent the Annunciation, the Nativity, the Arrival of the Santa Casa at Loreto and the Nativity of the Virgin, respectively. The treasury contains a large variety of rich and curious votive offerings. The architectural design is finer than the details of the sculpture. The apse is decorated with 19th century German frescoes, which appear to some as out of place.
The history of the house dates from at least the close of the crusading period. It is briefly referred to in the Italia Illustrata of Flavius Blondus, secretary to Popes Eugene IV, Nicholas V, Calixtus III and Pius II; it is to be read in all its fullness in the Redemptoris mundi Matris Ecclesiae Lauretana historia, by a certain Teremannus, contained in the Opera Omnia (1576) of Baptista Mantuanus.
According to this narrative, the house at Nazareth in which Mary had been born and brought up, had received the annunciation that she would bear the child Jesus, and had lived during the childhood of Jesus and after his ascension, was converted into a church by the apostles. In 336 the empress Helena made a pilgrimage to Nazareth and directed that a basilica be erected over it, in which worship continued until the fall of the kingdom of Jerusalem.
The narrative further states that, threatened with destruction by the Turks, the house was carried by angels through the air and deposited (1291) in the first instance on a hill at Tersatto (now Trsat, a suburb of Rijeka, Croatia), where an appearance of the Virgin and numerous miraculous cures attested its sanctity. These miracles were confirmed by investigations made at Nazareth by messengers from the governor of Dalmatia. In 1294 the angels carried it across the Adriatic to the woods near Recanati; from this woods (Latin lauretum, Italian Colli del Lauri), or from the name of its proprietrix (Laureta), the chapel derived the name which it still retains (sacellum gloriosae Virginis in Laureto). From this spot it was afterwards (1295) removed to the present hill, one other slight adjustment being required to fix it in its actual site. It is this house that gave the title Our Lady of Loreto sometimes applied to the Virgin. The miracle is occasionally represented in religious art wherein the house is borne by an angelic host.
Bulls in favour of the shrine at Loreto were issued by Pope Sixtus IV in 1491 and by Julius II in 1507, the last alluding to the translation of the house with some caution (ut pie creditur et fama est); While, like most miracles, the translation of the house is not a matter of faith for Catholics, nonetheless, in the late 17th century, Innocent XII appointed a missa cum officio proprio (a special mass) for the feast of the Translation of the Holy House, and as late as the 20th century, the feast was enjoined in the Spanish Breviary as a greater double (December 10).