1. The Ancient Christian Religious Center
2. The Vetus or Old Basilica and Baptistery of Santo Stefano alle Fonti
3. The Basilica of St. Thecla
4. The Baptistery of San Giovanni alle Fonti
5. The Basilica of Santa Maria Maggiore
It is believed that the most emblematic presence of Milanese Christianity was located – perhaps already in the 3rd century – at the site where Milan’s cathedral now stands. In fact, in 1386, the Duomo took root in ground that had been consecrated to Christian worship for more than a millennium.
Originally, the basilica, mentioned by St. Ambrose in a letter to his sister Marcellina, was most likely a “domus ecclesia” – a church that existed in a private home – with a large room located in the apsidal area of the Duomo. St. Ambrose referred to it as the “basilica iemalis,” the “winter basilica,” as opposed to the “summer basilica” of St. Thecla. This was the residence of the bishop, and where devotees would gather to celebrate the brotherly banquet, and the catechumens would come together to prepare for baptism. In short, it was a sort of first cathedral. Following the Rescript of Constatine and Licinius, promulgated in Milan in 313, the basilican complex underwent transformation. The basin of Baptistery of Santo Stefano alle Fonti, which was found at the end of the 19th century under the northern sacristy of the Duomo, dates back to that time. The foundation and the masonry of the octagonal basin are very similar to the ones of the more ancient apse of St. Thecla. If this is true, it was in this basin that the Bishop elect St. Ambrose was baptized in November, 374. It is likely that, from the 5th century onward, it became the women’s baptistery.
Ambrose spoke of a “basilica nova quae major est” – loosely speaking, a new and greater church – and it was the first actual cathedral built as such. It was large (67.6×45.3 meters), with a wide apse visible under the upper parvis, and its nave and four aisles extended under the present square. It can be dated back to approximately the third or fourth decade of the 4th century. Over the ages, it was subjected to changes, suffered fires and underwent restorations, until its gradual demolition during the 15th century (completed in 1461) in order to make room for the site of the Duomo, which, at that time, had only arranged the first five spans of pillars, beyond the transept.
It was the first Christian baptistery with a basin and an octagonal plan. The octagon symbolized the seven days of the creation and the eighth day, eternity, but also the eight Evangelical Beatitudes. St. Ambrose, who is said to have commissioned it in 378, probably drew inspiration for the octagonal plan from the imperial mausoleum of Massimiano. This way, when the catechumens entered the baptistery, they would have the sensation of entering a tomb where the old man within them would die and – as mentioned by St. Paul–rise again from the holy water. Inside, the baptistery featured eight niches, alternatively rectangular and semicircular, which overlooked the sides of the large central basin, and was accessible by descending three steps. Between the niches, in front of the buttresses which supported a large dome richly decorated with mosaic, stood porphyry pillars held up by a marble entablature. The excavations performed between 1961 and 1964 uncovered its layout, yet little had remained of the rising masonry. To get an idea of what the construction looked like originally, a stop at the Basilica of St. Lorenzo is recommended, where visitors can admire, both inside and out, the Chapel of St. Aquilinus. Built at the end of the 4th century, its measurements differ only slightly from the ones of the baptistery, and it has preserved its Roman identity entirely. It was in the font of San Giovanni that, during the Easter vigil of 387, Ambrose baptized St. Augustine. Just after the Duomo site had opened, the Fabbrica put up for auction pillars and marble from of the baptistery, which was demolished entirely in 1394.
Also known as the winter basilica, as it was smaller than St. Thecla and built with thick walls and a vaulting covering, it carried on with the tradition set by the Vetus basilica and became the second seat of the single cathedral. In fact, for more than a thousand years, Milan had a “dual” cathedral, alternating the liturgical celebrations between the two basilicas: from Advent to the Easter triduum in Santa Maria Maggiore, and in the following period, leading up to Advent, in St. Thecla. Santa Maria Maggiore was consecrated in 836 by the archbishop Angilberto II and it was considered the reconstruction of the Vetus, from which it inherited the title of Santa Maria Maggiore – St. Mary Major. It occupied more or less the area later taken up by the main nave of the Duomo, and was about seventy meters in length, with the apse located near the crypt of St. Carlo. It was completely destroyed a couple of times, rebuilt and expanded, but, as the Duomo site advanced, it was gradually demolished. For two centuries, its façade was the temporary façade of the Duomo. It was reused, disassembled and reassembled at least once to allow the progress of the naves and aisles and, eventually, it was definitively torn down at the end of the 17th century.