The basilica, in the town of Cagliari, overlooks a large square. The area on which it rises, at the foot of the hill of Bonaria, corresponds to the oldest Christian necropolis attested in the capital.
The title is recorded for the first time in a passage by the deacon Ferrando, biographer of Fulgenzio, the bishop of Ruspe who in the first quarter of the 6th century was exiled by King Trasamondo from North Africa to Cagliari, where he stayed twice and founded a monastery “iuxta basilicam sancti martyris Saturnini”.
The building would have been built as a 'martyrium' to honor Saint Saturnino, martyred in Cagliari in 304. The original structure was that of an early medieval cruciform church, with a central plan with four equal arms and a central domed body. The domed body and remnants of the quadrangular scarsella apse remain from this factory. The dome is connected by means of half-cross headphones (which perhaps replaced quarter-ball trumpets) to the square compartment, defined by arches in the middle that drain onto pillars with honeycomb columns in red African marble.
In 1089 the title was donated by Constantino-Salusio II de Lacon-Gunale, judge of Cagliari, to the Vittorini of Marseille, who rebuilt the monastery and established the seat of the Sardinian priory in San Saturnino. The monks were responsible for the restructuring of the church in proto-Romanesque forms between 1089 and 1119, the year of its reconsecration. During this phase, due to Provençal workers, the central domed body was maintained and the four arms were rebuilt, of which only the eastern one remains intact, with three naves and apse, with a bonaria limestone wall, hints of bichromia due to the insertion of volcanic ashlars and the use of marble remains. The middle aisle has a barrel vault set on a frame and punctuated by underarches, while the navatelle have cross vaults in cantonetti.
A manuscript by Carmona, from 1631, contains two drawings of the Romanesque building that was still intact, before the material used in the renovation of Cagliari's cathedral was removed from its ruined arms in 1669.

History of studies
Scholars disagree on the original naming, configuration and chronological placement of the early medieval plant. In 1953 Raffaello Delogu recognized in the church the typical pattern of the “martyrium”, the honorary building built with a cruciform plan on the burial of those who had sacrificed themselves for the faith. In 1978, Renata Serra, using the Delogu, gave the cruciform building to the first half of the 5th century. In 1979, Tatiana K. Kirova claims that the cruciform “martyrium”, assigned to the 6th century, had its arms drilled right from the original factory. In 1984, Letizia Pani Ermini identified in a mononave structure with an N-shaped apse, found under the cruciform church, the “basilica sancti martyris Saturnini” where Fulgenzio di Ruspe built the monastery at the beginning of the 6th century; towards the middle of the 6th century, the single-naved church would have given way to the cross-shaped one. There is greater agreement on the Romanesque restructuring, for which Delogu already identified ways of constructing the Franco-Iberian area due to the Vittorini of Marseille.

Bibliography 
R. Delogu, The Architecture of the Middle Ages in Sardinia, Rome, The State Library, 1953, pp. 8-13, 48-51;
T.K. Kirova, The Basilica of Saint Saturnino in Cagliari, Its History and Restorations, Cagliari, 1979;
L. Pani Ermini, “Research in the complex of Saint Saturn in Cagliari”, in Proceedings of the Pontifical Roman Academy of Archaeology. Rendiconti, LV-LVI, 1982-84, pp. 111-128;
R. Coroneo, Romanesque Architecture from the Mid Thousand to the Early '300, series “History of Art in Sardinia”, Nuoro, Ilisso, 1993, sch. 2; R. Coroneo-R.
Serra, Pre-Romanesque and Romanesque Sardinia, series “Italian Artistic Heritage”, Milan, Jaca Book, 2004, pp. 35-41, 44.
R. Serra, Studies on the Art of Late Antique and Byzantine Sardinia, Nuoro, Poliedro, 2004, pp. 95-96, 101-102; R. Coroneo, Romanesque Churches of Sardinia.
Tourist-Cultural Itineraries, Cagliari, AV, 2005, pp. 92-93;
R. Coroneo, “The Basilica of San Saturnino in Cagliari within the framework of 6th century Mediterranean architecture”, in Saint Saturnino Patron of the City of Cagliari on the 17th 100th anniversary of his martyrdom, Cagliari, 2005, pp. 55-83.