It's one of five Romanesque basilicas founded by Ambrose and it's one of the most ancient churches in Milan.

The building began in 379 and finished in 386, year when it was consecrate from Ambrogio and devoted to the Saints martyrs builted in the "the Martyrs' Cemetery." Four centuries later, in 789, the archbishop Peter founded a Benedictine monastery close to the basilica. Between the IX and the XII century, thanks to the archbishops Angilberto II and Ansperto the transformations started that shaped the Basilica, while later the pictorial decorations of the Bramante, Bergognone and Luini followed.

In September of 1395, in front of the basilica, Gian Galeazzo Visconti was crowned first Duke of Milan. In 1857 there was a radical static and artistic restauration with the consolidation of the structures to avoid further collapses to the vaults. The St.Vittore in Gold Sky was renewed and jobs were performed to the chapels and the bell tower of the canonries was restored. After the 1943 allied bombardments damages the basilica was object of a radical external improvement.

Of maximum interest are the pulpit, masterpiece of the first Romanesque period recomposed in 1201; the tabernacle, a rare work, based on four porphyry columns with marmoreal capitals adorned of colored plasters of working Byzantine lombardo; the golden altar (protected from a crystal urn), gift of the archbishop Angilberto II; the carved wooden choir, of slow-Gothic style, with polychrome carvings that recalls scenes of the St.Ambrose life and allegorical scenes.
The basilica of St.Ambrose also boasts a formidable frame of chapels where the existing styles to Milan are represented.

It is worth to visit the of St.Ambrose museum, rich of the funeral monument relics of the Della Croce and some "Monks whiners" of Burgundian school.