The Cathedral of Albenga stands at the geometric center of the Roman city and most likely dates back to the period of reconstruction by general Constantius, later emperor Constantius III. The Cathedral, with the Baptistery, remains to this day the center of the Christian community of the city and of the vast diocese, albeit with alternating phases of adaptations and reconstructions. It therefore constitutes an extraordinary example of continuity of building and worship, from late antiquity to the present day, with construction phases known following the stratigraphic excavations carried out on the entire extension of the church in the years 1965-67; from the first late Roman church, with three naves and a basilica plan, in the early Middle Ages the central nave was used with the abandonment of the side aisles, which remained cemeterial and road trampling areas. The recovery begins between the 11th and 12th centuries, in Albenga as in many Roman and bishopric cities, first with the organization of the Marches and the Committees, then with the formation of the Municipality, a period marked by the recovery from maritime activity and towards the hinterland . Even the cathedral, the first seat of the Municipality, was restored to its initial size with an important reconstruction phase, and with this aspect it remained the center of the life of the city and its vast territory for a long time. In the sixteenth century the bad conditions of the church and the new rules of the Council of Trent led to its restructuring in sixteenth-century forms, with the raising of the floor, the incorporation of the columns into massive pillars, the cutting of the ancient arches, the opening of new ones. large windows in the central and side aisles, the reconstruction of the vaults. The radical restoration of the sixties of the last century consolidated the building, already at serious static risk due to the cutting of the medieval arches, and left the various phases of the monument visible.
On the outside, the central and lower part of the façade belongs to the early Romanesque phase, raised in the municipal period and enlarged on the right and on the top by the new facing in larger ashlars; in the center, small pillars with sculptures from the same phase that flanked a multi-lancet window which was then buffered; the rose window is from the early twentieth century. The bell tower, built outside the central nave in the early Romanesque age, and included in the left aisle with the communal age, was unsafe at the end of the fourteenth century, and was rebuilt between 1393 and 1398 (all documentation is preserved); is a beautiful example of late Gothic in Liguria.
Inside, the works of the 1960s have left parts of the different phases of the church visible (the late Roman and early medieval ones are preserved under the current floor and visible under the high altar, in particular the remains of the late ancient monumental altar ): the columns were brought to light with the beginning of the Romanesque-Gothic arches and the arches were rebuilt, the apsidal area, raised, has remains of various phases of medieval frescoes; the modern table is supported by the marble bas-relief formerly of a noble chapel, with the saints Michele, Giovanni Battista and Verano. The left apse, used in the early Romanesque period as a chapel outside the church, preserves the floor and base of the altar, while in the right apsidal chapel the only seventeenth-century altar, formerly in the church of San Bernardino, preserves a remarkable panel of Pentecost, attributed to the painter from Pavia Pietro Francesco Sacchi.
The Cathedral in the centuries between the sixteenth and eighteenth centuries had been enriched by numerous altars, important works of Genoese marble workers, today unfortunately dispersed in churches of the diocese. Finally, at the end of the nineteenth century the interior, previously clear, was entirely decorated by Genoese frescoes. On the wall of the right aisle, after an ogival door that leads to the Sacristy (a beautiful vaulted structure from 1511, with busts and tombstones of bishops), there is the tombstone of the bishop Leonardo Marchese (1513), a cultured humanist, who endowed the church of splendid illuminated manuscripts; near the door of the right aisle, a late medieval aedicule with a fresco of Santa Margherita. The monumental organ on the counter-façade is remarkable: the wooden structure is the work (1614-1617) of the brothers Gio. Giorgio and Pietro Botto, initiators of the well-known dynasty of wood sculptors who worked in Turin for more than a century; the instrument placed in the case is an important work of the Serassi brothers of Bergamo (1840).