The Basilica of Saint-Sernin is a Romanesque basilica located in the city of Toulouse, in the south of France. It was built between the 11th and 13th centuries and is considered one of the most important Romanesque structures in Europe.

The basilica is dedicated to Saint Saturnin, the first bishop of Toulouse, who was martyred in the 3rd century. It is located on the site where he was said to have been buried.

The basilica is built of brick and stone and has a distinctive octagonal bell tower. It has a cruciform plan with a nave and four aisles, which are separated by rows of columns with sculpted capitals. The interior is richly decorated with frescoes, carvings, and stained glass windows.

One of the most striking features of the basilica is its ambulatory, which is lined with radiating chapels. The chapels contain many important works of art, including a reliquary of Saint Saturnin, a 12th-century statue of the Virgin Mary, and a 14th-century altarpiece.

The basilica also contains a number of tombs, including those of Saint Saturnin and Saint Sernin, a bishop of Toulouse in the 6th century.

The Basilica of Saint-Sernin is a UNESCO World Heritage site and is an important destination for pilgrims and tourists alike.