Sant'Orso had originally a single hall, delimited by a semicircular apse. It was entirely rebuilt during the 9th century, during the Carolingian age. Later, bishop Anselm of Aosta further renovated the church, introducing a basilica plan with three naves with wooden trusses. These were replaced by Gothic cross vaults in the 15th century.
The church has a nave and two aisles divided by quadrangular pillars.
The vault was rebuilt in the 15th century. Fragments of a Romanesque series of paintings are preserved in good condition in the space between the current vault and the original ceiling. These portray scenes from the New Testament as well as a martyrdom. Stylistically they resemble the bright colours and strongly marked outlines of some of the frescoes at the Galliano Basilica near Cantù. In the right aisles is a chapel houseing the altar of St. Sebastian, also with frescoes (15th century).
The cloister has historiated capitals depicting the life of Ursus. 37 of the 42 original capital remains: they were originally in white marble, though now they mostly appear in dark gray color aftery they were washed with ash paint.
The quadrangular-plan bell tower, dating to 989, has kept some the lower 15 metres of the original medieval structure. The present structure, in Romanesque style, dates to the 12th century, and has a total height of 44 metres.
The church is home to numerous missals and reliquaries, including the relics of Ursus, which rest in the crypt. It also holds the relics of Saint Gratus of Aosta.
References:The Cathedral of Saint Mary Major, often called Lisbon Cathedral or simply the Sé, is a Roman Catholic cathedral located in Lisbon, Portugal. The oldest church in the city, it is the seat of the Patriarchate of Lisbon. The cathedral has survived many earthquakes and has been modified, renovated and restored several times. It is nowadays a mix of different architectural styles.
The site where it stands was the principal mosque of Lisbon when it was an Arab settlement. The construction of the cathedral started around 1150, three years after the city was conquered from the Moors during the Second Crusade. Shortly after the victory the English knight Gilbert of Hastings was named bishop of the city of Lisbon.
One good reason to visit the Cathedral is to visit its charming cloisters located in the back. There are several tombs in the cathedral, the most notable of which is the beautifully sculpted tomb of Lopo Fernandes Pacheco and his wife.