The oldest trace of settlements in the area were found in the surroundings of the Pieve del Cauro (7th century), an old parish church under the influence of the Monastery of Saint Quintino of Spigno Monferrato, now in ruins just outside the hamlet Piana. This church was likely built on an ancient Roman statio placed along the Via Aemilia Scauri.
In the 11-13th centuries, due to the increase of trade along the ridge route between the Po valley and the Ligurian Sea and the need to provide a better military defence, the current medieval village of Montechiaro Alto (Mons Cauri) was built. In that period, marquis Delfino del Bosco ceded the authority on Montechiaro to the city of Alessandria. However, in 1284 the inhabitants brokered a treaty with marquis Del Carretto.
Then ruled by the Duchy of Milan, after the death of Filippo Maria Visconti (1447) Montechiaro was occupied by the armies of Francesco Sforza. Since 1454 the fief was ceded to the noble families of Del Carretto of Bossolasco and then to Scarampi di Cairo Montenotte. New trades and sales led to the rule of the Marquis of Canelli, the Scarampi-Crivello, the Cavoretti of Belvedere and the Gianazzo of Pamparato, which maintained the feud even after the oath of allegiance to the House of Savoy (1736). Since 18th century, Montechiaro was part of the Kingdom of Sardinia, the Kingdom of Italy and, finally, of the Italian Republic.
