The sanctuary occupies an ancient round building of Roman construction dating back to the 1st century, traceable to Domitian's villa at Castel Gandolfo,[2] which was formerly a nymphaeum[3] or, according to other hypotheses, a temple.

[6] The erection of the building with a perfectly cubic plan within which a sphere is inscribed, later to be used as a sanctuary, is dated by all scholars to the imperial age, under the principate of Titus Flavius Domitian (81 - 96).

In the course of the earthworks in the 1930s, a layer of soil mixed with wheat seeds was found: this would suggest a continuation of pagan worship in the last centuries of the empire,[13] and would exclude that consecration as a Christian church took place immediately at the time of Constantine the Great.

[13] There is a tradition in the Volgo Albanense, that in this persecution some of those fleeing Greek Nuns withdrew to their City, that they brought with them that Image of our Lady, today called of the Rotonda, and that they exposed it to public veneration in that round Temple, at other times dedicated to Minerva [...].It is widely believed that the Christian sanctuary was founded by Eastern-rite religious devoted to iconodulism who fled the Byzantine Empire at a time when iconoclasm was raging.

[4] In any case, the first consecration of the sanctuary of which there is any record took place on December 7, 1060, when Pope Nicholas II was reigning: the church was dedicated in ancient Greek to the Most Holy Mother of God.

[23] Thus it was that in 1369 a dispute arose between the free commune of Velletri on the one hand, and on the other the Guglielminian monks of the church of San Paolo and the Augustinian nuns of the Rotonda, both supported by the cardinal bishop of Albano, Angel de Grimoard.

[24] Pope Urban V, from Avignon, appointed the cardinal bishop of Sabina Guillaume d'Aigrefeuille the Younger as judge-commissioner to investigate the affair: it is unknown how the dispute ended.

Subsequently, on June 15, 1444, the destroyed and abandoned churches and convents were granted by Eugene IV himself to the Girolamini religious of the basilica of Saints Boniface and Alexius in Rome: among them, the sanctuary of the Rotonda with all its annexed and related property is also reported.

[28] However, as early as during the apostolic visitation of Monsignor Marco Antonio Tommasi in 1661, a neglected situation of the sanctuary was attested,[16] whose jurisdiction still belonged to the Girolamini monks of the basilica of the Most Holy Boniface and Alessius.

Thus, the cardinal bishop of the suburbicarian see of Albano Giovanni Battista Pallotta decided to challenge the apostolic constitution Instaurandae regularis disciplinae issued in 1652 by Pope Innocent X - "super soppressione parvorum conventuum, ac prohibitione erigendi novos" (i.e., "on the suppression of small convents and the prohibition of erecting new ones")-:[29] therefore, on August 6, 1663, the diocese purchased the convent and some surrounding dwellings from the Girolamini monks for the price of 1250 scudi.

[30] Further work on the interior of the sanctuary was carried out with funding from Cardinal Bishop Virginio Orsini in 1673,[31] who had the lantern built on the central oculus of the dome and had it covered with lead.

[30] Pope Clement XI, by a papal brief dated June 19, 1708, granted the religious congregation of the Poor Clerics Regular of the Mother of God of the Pious Schools -widely called Piarists- the management of the bishop's seminary and the sanctuary.

[35] After the French occupation of Rome on February 9, 1798, and the consequent proclamation of the Roman Republic on February 15, Frascati, Marino, Albano and Velletri formed themselves into as many autonomous republics twinned with the Roman one:[36][37] just as in April 1798 a government commissioner took charge of the recovery of all the valuables from the sanctuary of Santa Maria di Galloro in Ariccia,[38] so too was the case at the sanctuary of Rotonda, from which the Piarist monks had been expelled under the suppression of religious orders.

[34] Between May 21 and December 5, 1829 as many as 248 earthquake tremors shook the area of the Alban Hills:[39] the population of Albano, noting the small amount of damage to people and buildings, thought to attribute this to the intercession of Our Lady of the Rotonda,[40] so much so that between August 22 and 30 of that year solemn celebrations were held for a new coronation of the image at the cathedral basilica of San Pancrazio.

[43] In 1931 a city committee was created to promote restorations to the dome of the sanctuary:[44] the Regia Soprintendenza ai Monumenti per il Lazio thus had the first work done on the structure, finding, however, considerable problems in the entire building.

We thus have a small Pantheon, representing the same proportions between plan and elevation, in that the section is a perfect circle and the vault is built in horizontal layers, without ribs or arches: a round hole in the middle increases the light, while a well in the center of the floor, provided with a long burrow, conveyed rainwater to the drain.The building was most likely built during the reign of Titus Flavius Domitian (81 - 96) and belonged to the complex of Domitian's villa, the ruins of which are for the most part incorporated into the present papal villas of Castel Gandolfo.

[7] At the time of its construction, the building's interior consisted of a cylinder inscribed in a cube and covered by a hemisphere, all built entirely of opus mixtum in the likeness -reduced in scale- of Rome's Pantheon.

With the readaptation into a place of Christian worship, the four Roman niches were converted into chapels; in the 14th century the sanctuary was enriched with frescoed pictorial cycles, such as the History of the True Cross[52] and St.

[47][48] In the 18th century, as shown in an engraving by the painter Carlo Labruzzi (1748-1817),[55] the facade was simply a plastered wall on which opened a door surrounded by fine Roman marble entablatures; two of them were photographed by Lugli,[56] while currently one of them, measuring 1.70 x 1.00 x 0.50 meters,[41] supports the high altar mensa.

In 1878 the cardinal bishop of the suburbicarian see of Albano Gustav Adolf von Hohenlohe-Schillingsfürst contributed financially, together with the Albanese community and wealthy villagers,[41] to the construction of a new facade for the sanctuary, of Doric order, designed by architect Mariano Salustri.

[47] On November 15, 1951, a contract was signed with the architect Perenzio and the company Mengoni, and work began:[47] the existing holes in the lower part of the bell tower were walled in, cosmatesque tiles were added, and the cornice was completed.

During excavations in 1919, in fact, a row of four blocks of white marble and one of peperino 60 centimeters wide, which may have belonged to the threshold of a Christian altar, was discovered at a depth of about 1.95 meters below the floor of the then church.

[59] During the 17th century, several works were carried out in the niches: for example, in 1616 the Roman citizen Lelio Santori had an altar dedicated to St. Charles Borromeo built on the right wall of the sanctuary.

[34] The present high altar, reconsecrated on August 5, 1938, is supported by the aforementioned marble fragment of a cornice from the imperial age, which until 1878 served as the entablature of the sanctuary door.

[41] The ambon consists of an Attic column base surmounted by a composite capital and fragments of Byzantine and Romanesque cornices, all of which were found in the earthwork of the sanctuary during the restorations.