Founded in 379 as Basilica Martyrum on the burial spot of the martyrs Gervase e Protase, in 397 the basilica also became a mausoleum for the city's bishop and future patron saint. Because of this - a testimony to Milanese ecclesiastical independence, and its ancient traditions - the church is one of the most symbolic sites in the city. By the 11 th century the edifice was extensively rebuilt in the Romanesque style. A vast arcaded atrium, built between 1088 and 1099, gives entrance to the Basilica. The atrium has a rectangular plant, three sides of which are arcades while the forth is the narthex of the basilica. There are composite columns with decorated capitals, engraved with figures representing different kinds of monsters and vegetables, dating for the most part from the 17 th century.In the inside high pillars hold arcades, the central of the three of apsidal naves is divided in four square spans; the aisles on the sides are identical and topped by the women's galleries. Many frescoes and mosaics of high value are present, like the seventh chapel that gives access to the small chapel of Saint Vittore in Ciel d'Oro. The gabled form of the façade on two superimposed loggias, a narthex, and an upper loggia of five diminishing arches, seems to be framed at the base by the arcades of the atrium itself; while the higher part is flanked by the double profile of the bell towers, the southern and shorter one is called the Torre dei Monaci, and dates from the 9th century, while the second one, incorporating delicate pilasters and small arches, is known as the Torre dei Canonici and was built between 1128 and 1144. On the left portal a pre-Romanesque relief depicting St. Ambrose is found; the central portal has lintels, door posts, and lunette formed by intaglio fragments dating from 8th - 10th century.