The Marian basilica built by Sixtus III (432–440) is the only one among the great churches of Rome to have remained substantially intact in its structure, as well as in parts of its iconographic program. The nave – divided into three aisles by two rows of columns each supporting an architrave – was originally closed to the west by an apse, probably extended further west by a kind of ambulatory. Thus, there was no transept. During the medieval and Baroque periods, modifications were made to the building, but they did not radically alter its existing core. The significance of Rome’s first Marian church was enhanced by the popularity of the cult of the Nativity (Santa Maria ad Praesepem), as well as by the miraculous icon of Mary (the icon of the Evangelist Luke), which occupied the highest rank among the Marian images of the city and which was visited in procession by the ‘Icon of the Savior’ from the Lateran and by other images of the Virgin. Of the rich liturgical furnishings of the early Middle Ages (Pope Paschal I, 817–825), which also included the raising of the altar area, no traces have survived. Between 1100 and the early fourteenth century, the liturgical furnishings were updated and renewed in several campaigns, though much of their outcome was later altered by Baroque renovations, especially those carried out by Ferdinando Fuga under Pope Benedict XIV (1743–1750). At the beginning of the twelfth century, a bell tower was built, which was later replaced in the fourteenth century by the one still standing today. The eastern façade was embellished under Pope Eugene III with a new portico. The ambo erected under Pope Alexander III suggests a renewal of the schola cantorum. At the end of the century, the financing of the opus sectile pavement in the central nave by the Paparone family probably marked the temporary conclusion of the works. It is only in relation to this period that the legend of the miraculous snowfall in August – with which Mary was said to have designated the site and dimensions of her future church – is attested. The story became extremely popular in the following centuries and spread widely. The thirteenth-century renovations began in the latter part of the century. In 1256, Jacopo di Giovanni Capocci and his wife Lavinia donated an altar with a tall ciborium-reliquary, serving as the pilgrims’ altar, in the central nave. In the fourteenth century, as a pendant, another altar with ciborium was erected to house the icon of the Virgin. The first and most extensive medieval remodeling was initiated by Pope Nicholas IV and his protector and patron, Cardinal Jacopo Colonna, archpriest of Santa Maria Maggiore. The apse was demolished and rebuilt seven meters further west. Between the nave and the new apse, a narrow transept was inserted, whose painted decoration was carried out only on the upper parts of the southern arm. It is possible to hypothesize that the transept of Santa Maria Maggiore was built with reduced width in order to preserve the dimensions of the basilica as established by the Virgin, without exceeding those marked by the presumed western ambulatory. The works proceeded in parallel with the reconstruction of the apse, transept, and eastern façade of San Giovanni in Laterano, a project also undertaken during the pontificate of Nicholas IV, at least partially by the same workshops active in Santa Maria Maggiore. Here, the apse mosaic depicting the Coronation of the Virgin was signed by Jacopo Torriti in 1296. Through its synthesis of Roman tradition and contemporary Gothic tendencies, the work represents a highly significant moment in medieval painting. The apse cylinder is decorated with scenes from the Life of the Virgin, while on the exterior, a Marian-themed mosaic cycle adorned the cornice of the apse. At the same time, on the eastern side, a new façade was erected, also entirely covered with mosaics. The Deesis with saints and the tetramorph in the lunette was signed by Filippo Rusuti. Two cardinals of the Colonna family were represented as founders: one of them is identified in the inscription as Jacopo. The four scenes of the founding legend represented on the lower surface are clearly attributable to the patronage of the Colonna family, as evidenced by the numerous coats of arms. Although the power of the Colonna was violently suppressed during the pontificate of Boniface VIII, it is still possible to identify a “Colonna era” in relation to the construction and decoration of Santa Maria Maggiore during the years 1288–1296 and ca. 1305–1315. In the new extension of the western area (north transept and apse), the funerary monuments of Pope Nicholas IV and the two Colonna cardinals were placed; thus, it is possible to hypothesize that one of the motivations for the restructuring was the creation of a family memorial space in proximity to the tomb of the pope who bore their name. During the pontificate of Nicholas III, the interior of the Cappella del Presepe was also remodeled, and it was reconsecrated in 1291. After the transfer of the small devotional space to the new Sistine Chapel (1587, by Domenico Fontana), only the altar frontal and most of the small statues from an Adoration of the Magi – identified as works by Arnolfo di Cambio – remained. This contribution proposes a new reconstruction hypothesis concerning the debated original arrangement of the figures of this group. Each of Rome’s great churches can be understood as a structure shaped by history and as a mirror of dominant social dynamics, particularly among the noble families of the city. Santa Maria Maggiore offers especially significant evidence for the twelfth and thirteenth centuries (Paparone, Capocci, Colonna, Savelli, Normanni). The usual distinction between ecclesiastical and lay patrons appears to have been of secondary importance compared to a mentality that valued family ties and client networks. In particular, the legend of Santa Maria Maggiore – according to which both a pope and a noble couple were chosen together by the Virgin for the foundation of the first Marian church in the area designated by the miraculous snowfall – seems to have been used as an effective propaganda model. It indeed encouraged joint action by members of noble families, whether lay or ecclesiastical.