A carroccio (Italian: [karˈrɔttʃo]; Lombard: carrocc [kaˈrɔtʃ]) was a large four-wheeled wagon bearing the city signs around which the militia of the medieval communes gathered and fought. It was particularly common among the Lombard, Tuscan and, more generally, northern Italian municipalities. Later its use spread even outside Italy. It was the symbol of municipal autonomy. Priests celebrated Mass at the altar before the battle, and the trumpeters beside them encouraged the fighters to the fray.

Defended by selected troops, paved with the colors of the municipality, it was generally pulled by oxen and carried an altar, a bell (called martinella), the heraldic signs of the city and a mast surmounted by a Christian cross. In peace time it was kept in the main church of the city to which it belonged.

In battle the carroccio was surrounded by the bravest warriors in the army as the carroccio guard, and it served both as a rallying point and as the palladium of the city's honour; its capture by the enemy was regarded as an irretrievable defeat and humiliation.

The carroccio, which has Lombard origins, was initially used by Arimannia as a war chariot. Its function became purely symbolic, with the addition of the cross, of the city signs, of the altar and with its preservation in the main church of the city between 1037 and 1039 due to the Archbishop of Milan Aribert's use in one of the sieges that Conrad II, Holy Roman Emperor did on several occasions in Milan. The carroccio therefore, from a military means, became a purely political instrument. From Milan its use spread in many municipalities of northern Italy, in Tuscany and outside Italy, until the decline in the 14th century. Medieval documents show the carroccio called carochium, carozulum, carrocerum or carrocelum, while in the Milanese dialect of the time it was probably called caròcc or caròz. The carroccio was introduced by Heribert (Ariberto) for use as the military insignia of Milan. His many supporters adopted and spread the use of the insignia. It was soon adopted in Lombardy, Tuscany and Rome where it signified a militia aligned toward a defence of the Church.

Its diffusion extended to other Lombard cities, but this cannot be explained as a pure reproduction of the Milanese carroccio. Moreover, the descendants of the Arimannia, still at the turn of the 11th and 12th centuries had maintained, in the medieval society of northern Italy, a certain autonomy and were recognizable for various specific prerogatives, although the Lombard domination had ended after a few centuries.

Documents of 1158 and 1201 confirm the presence of the Milanese carroccio, in peacetime, in the church of San Giorgio al Palazzo, while others are still inside the Palazzo della Ragione. The first document cited contains information on the need to make an iron shield to be placed in the choir of the church, which was located near the carroccio, with the lighting of a votive fire fed by a pound of oil. The 1201 document contains similar information in that the archbishop of the San Giorgio al Palazzo church in Milan should have lighted votive lamps around the carroccio.

In 1159 the municipal troops of Brescia conquered the carroccio of the Cremona area during a battle. The cart was then carried in triumph between the streets of Brescia and was placed in the community church, with the "martinella" which was positioned on the civic tower of the city.

The carroccio was the protagonist in the battle of Legnano on 29 May 1176, during which it was defended, according to legend, by the Company of Death led by Alberto da Giussano, a fictional character who actually appeared only in literary works of the following century. According to the legend, during the fight, three doves, out of the burials of the saints Sisinnio, Martirio and Alessandro at the basilica of San Simpliciano in Milan, rested on the carroccio causing the flight of Frederick Barbarossa.