The Basilica of San Lorenzo Maggiore was originally built in Roman times and is one of the oldest churches in Milan.
The basilica was built between the late fourth and early fifth centuries. The exact date is uncertain, as are the name of who commissioned it and the circumstances of its foundation. What is certain is that at the time of its construction the basilica was the largest, centrally planned building in the West. The dedication of the temple to St. Laurence (San Lorenzo) the martyr has been certified only from 590, when Milan was already controlled by the Lombards.
The eleventh and twelfth centuries were marked by numerous disasters: fires, in particular the terrible “fire of the Stork”, that in 1071 devoured the basilica, devastating the internal decorations, and earthquakes, that undermined the stability of the complex, making new restorations necessary between the twelfth and thirteenth centuries. Towards the middle of the eleventh century, the open space behind the basilica, called Vetra, was used as the place of executions: this practice continued until 1840. By 1167, with the construction of the medieval walls, the basilica was to be found within the city, at the new Porta Ticinese (Ticinese gate).
The basilica of San Lorenzo remained throughout the Middle Ages a symbol of the legacy of the Roman Empire in Milan. Subsequently during the age of the Renaissance, especially after the 1154 destruction of the other Ancient Roman structures by Emperor Barbarossa, the temple was an example of the classical architectural canons admired by humanists, and studied by architects and artists such as Bramante, Leonardo, and Giuliano da Sangallo. Painted references to the church from that era can be identified.
On 5 June 1573 the dome of the basilica suddenly collapsed. Construction of a new dome in a more modern style began immediately and were completed in 1619. During the reconstruction, a miracle occurred, one predicted by Archbishop Carlo Borromeo: one year after his death in 1585, a sick woman was cured in front of the icon of the Madonna del Latte, displayed on the Piazza della Vetra. Following this event, donations increased enabling more rapid progress in the reconstruction. In 1626, the Madonna del Latte was transferred to the high altar where it remains to this day.
In the 1830s the Austrian Government began a redevelopment of the Vetra: houses built leaning against the basilica and inhabited by tanners were demolished; the channel of the Vetra was covered over; and executions were abolished. After the bombings of 1944-1945 the houses that had been destroyed were not rebuilt enabling the park of the basilicas to be created, from which there is an excellent view of the complex. In 1934 in place of the demolished houses a sort of a courtyard was formed, with the creation of a public square opposite the basilica.
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