In the ninth century, Alcuin of York, cultural advisor of Charlemagne, aptly defined Ambrose as ‘defensor civitatis’, defender of the city and people of Milan. It was during this period that the Milanese Church was first called the Ambrosian Church, in a letter by Pope John VIII. The identity between patron saint and the city consciousness remained constant throughout the entire Middle Ages. Not only had the legacy of Ambrose generated a unique liturgical rite that is still used today, but it also became a civil and political emblem, to the point that the image of the patron saint was emblazoned on the gonfalone del Carroccio, the banner of the chariot carried into battle by the Milanese in the medieval period and also celebrated during the Risorgimento.
The earliest visual representation of St Ambrose is found in the wall mosaic in the sacellum of St Satyrus (fifth-sixth century). Here, the bishop is wearing a dalmatic with clavi (long vertical stripes descending down the front and back from the shoulders) and portrayed with realistic features as the governor of Milan. In the Middle Ages, the iconography of Ambrose followed that of the bishop saint, with mitre, crozier and open book, upon which he is sometimes shown writing, inspired by the Holy Spirit. At the end of the eleventh century, Ambrose started to be portrayed holding a scourge, symbolising the fight against heresy. In the fourteenth century he also began to be shown riding a white charger, trampling the city’s enemies, an image promoted by the Visconti, after the Battle of Parabiago in 1339.