The Basilica was built on a cemetery of the III-IV century AD and it's dedicated to Eustorgio I, first Bishop of Milan. The original Basilica had longitudinal plant, perhaps covered by a barrel vault, but the actions of the thirteenth century led to radical changes in the existing space: the church developed a raised "in the room" and was enriched in the pulpit, apse, of an arm of the transept with two chapels and the entire roof with cross vaults. Since 1234, it was one of the venues of the Inquisition of Lombardy. Under the Visconti family received numerous commissions: chapels, a new library, the high altar, the refectory and the cloister. Over the centuries, many families have commissioned funeral monuments and works of art for the Basilica: the Portinari have commissioned the chapel for the relic of St. Peter Martyr; in the fifteenth century is the time of the Brivio chapel, with the altarpiece of the "Madonna and Child with St. James and St. Henry", by Bergognone, and Tomb of Giovanni Stefano Brivio. After the years of the Inquisition, the complex takes on new importance thanks to Carlo Borromeo. Between the sixteenth and eighteenth century the Basilica was enriched with works of important Lombard artists (Campi, Urbino, Pellegrini, Daniele Crespi, Fiamminghino, Francesco Croce, Antonio and Giovanni Battista Lucini Marone). In the nineteenth century, major renovations concerned the facade, the input and the chapels. After the acquisition of the City of Milan, the complex houses the Diocesan Museum.