I recently visited the San Eustorgio church after a long time. Here I would like to focus in particular on two attractions that it contains, and which are probably the ones drawing most of the visitors.
The first attraction is the Tomb of the so-called Three Kings ("Re Magi" in Italian). Giant sarcophagus, it bears the inscription “Sepulcrum trium magorum” (which, however, was only added in the 18th century). An explanatory panel at the sarcophagus summarizes the tradition of their translation from Constantinople in 343 AD, and the subsequent (instead well documented) transport to Cologne in Germany in 1164, as war prey that Emperor Frederick I Hohenstaufen took from the city of Milan after its surrender.
The alleged relics of the Three Kings are still found in Cologne (the imposing cathedral of the city was started to house them), so what you see is an empty sarcophagus. However, it invites us to learn more about the history of the Kings, to distinguish the facts somehow documented from inventions (many) and to deepen the allegorical meaning of their history: alluding to a Christian revelation that is also addressed to "gentiles" (= non-Jews), originally first of all those from Eastern world.
The Portinari Chapel is quite different. It, linked to the church but well distinct from it from the architectural point of view, shows a quadrangular plan surmounted by a dome, which as such recalls the Old Sacristy of the church of San Lorenzo in Florence, by Filippo Brunelleschi; but otherwise it differs from the sobriety of the original to graft onto this structure decorative elements typical of the Lombard Renaissance (Certosa di Pavia, Colleoni Chapel in Bergamo): above all the dancing angels in terracotta on the dome drum, and the dome itself covered by polychrome scales. In my opinion, this synthesis is wonderful.
The chapel has not been attributed with certainty to an architect. Today the name of Guiniforte Solari (1429-1481) is considered: he shaped the Milan of his time, thanks to the role he had in the main buildings in progress.
The admirable frescoes on the walls, regarding the life of St. Peter "the martyr", are the work of another illustrious Lombard, Vincenzo Foppa, while the sepulchral ark of the saint, in the center of the chapel, is a work of the fourteenth century, later transported here , and it is probably due to Giovanni di Balduccio (Pisa, 1300-1349). The Chapel as a whole therefore documents, among other things, the transition from the era in which Lombardy was a tributary [also] of the Tuscan artists, to the era when the Lombard Renaissance was fully autonomous.