The name Sernin evolved over the centuries from the name of the ancient Roman patron saint of the Basilica, Saturninus.
Built between 1070 and 1300, the church building is remarkable for its size. Its length (115 metres), its 5 naves, and its transept (64 metres) make it one of the largest of all romanesque churches. The romanesque style of its original design, maintained all through its long history, has assured for the building its unity. More than 400 capitals adorn the church.
The basilica tells the story of the Christian faith. Its plan in the shape of a cross recalls that the Church was born from the sacrifice of Christ, who died on the Cross. The building is turned to the East to express Christ Resurrection, cosmically symbolized by the rising Sun.
The 12 crossings of the nave may figure, besides the 12 Apostles, the diversity of the peoples within the unity of the Church. The 72 pillars represent the 72 disciples sent by Jesus on mission. The 5 naves are typical of all the great romanesque basilicas. The length of the transept, a measurement taken from the old basilica of Saint Peter in Rome, expresses a particular fidelity to the Pope.