The name Carroxium appears for the first time in a document from 1144. In 1185, however, with a sentence promulgated by Emperor Frederick II, the road between Voltaggio and Gavi (therefore passing through Carrosio) was declared free to Italian merchants .
However, the high taxes applied by the marquises of Gavi forced the merchants to look for an alternative route: for this purpose the old settlement of Meo was perfect, easily defensible due to its elevated position and an excellent "hub" for travelers towards Rigoroso.
In 1144 the lords of Montaldeo gave allegiance to the Superba half of their fiefdom and guaranteed the possession of Voltaggio, Fiaccone (today Fraconalto) and Amelio (another name for Meo); two years later, the lords of Gamondio (now known as Castellazzo Bormida) undertook to assist Genoa in the management of the three possessions.
Throughout the 12th, 13th and 14th centuries this road thus constituted the transversal link that connected the Lemme and Scrivia valleys, with the approval of the Consuls of the Republic of Genoa.
The decline of Aimero (Meo) and the "rebirth" of Carrosio
The increase in landslides and the progressive decrease in the importance of Aimerio (also cited as Amelio in documents of the time) due to the ever-increasing passage of merchants towards the road along the Lemme, facilitated by the agreements with Gavi, caused a rapid decline of the settlement, with its inhabitants who spread out in the nearby settlements: the most "chosen" one was precisely that of Carrosio.
Some family groups maintained their Amelio origins in the surname: among these the Ameri, the Amelio and the Imelio. In the following centuries, these surnames often appeared in the documents of noble families and in the registers of the Church, among high local offices[6]; in the meantime, the village grew at a slow but steady pace.
In March 1625 the Franco-Savoyards commanded by Carlo Emanuele I of Savoy invaded the territory of Carrosio, facing the Genoese allied with the Spanish. At first they won, breaking through the defense lines of the Ligurians, but they were subsequently stopped in Malpertuso, near Montanesi, where today the Sanctuary of Our Lady of Victory stands, and on 21 June 1625 they definitively abandoned Carrosio.
Passed to the Savoy family in 1735, it became a Savoy enclave within the Republic of Genoa. Once the fiefdom was abolished in 1798, he was the protagonist of a Jacobin revolt against the Piedmontese government, which resulted in an attack on the castle of Serravalle - which failed - by 2000 revolutionaries; the survivors were hunted down by the inhabitants of nearby towns and killed "like unbelieving men and enemies of all authority".
After the Napoleonic victories and the reconstruction of the Ligurian Republic, Carrosio became part, with a decree of 4 September 1802, of one of the 18 cantons of the "Lemo jurisdiction", with a municipality and three justices of the peace.
Three years later, the Ligurian Republic was incorporated into the French empire, and French laws and practices also became in Carrosio: the mayor was called "Maire" and official documents had to be drawn up in French.
In 1812, Pope Pius VII, headed for exile in Fontainebleau, was hosted in the "Roccone" of Carrosio: a plaque walled in the front of the building bears witness to this.
After the fall of Napoleon, at the Congress of Vienna the annexation of the Republic of Genoa to the Kingdom of Sardinia was decided: the country therefore definitively returned to the Savoy dominions, and on 2 September 1815 King Vittorio Emanuele I and Queen Maria Teresa d 'Austria-Este crossed Carrosio, greatly celebrated by the local population[7].