The area that was called Le Murelle was the site of the ancient Etruscan city of Rega which then became ‘Regis Villa’ in the Roman period. It was a small settlement of farmers and fishermen near a port, fully submerged today, where plied the commercial traffic of the nearby and important Vulci.
The current village dates back to medieval times and was built on a hill to defend themselves from the incursions of the Saracens: ‘Castrum Montis Alti’ was founded in the V-VI century AD.
According to some legends it was founded by refugees from the coastal city Gravisca, destroyed by pirates, while others say that the castle was founded in the eighth century by Desiderio, King of the Lombards. In any case, the Castrum “Montis Alti” is mentioned for the first time in a papal bull of the ninth century, where it is listed among the possessions of the Apostolic Camera.
Between the eleventh and twelfth centuries Montalto was seriously damaged such as that of 1109 when Pope Paschal II had the castle where it Stefano dei Corsi was hiding destroyed by Norman Norman. For many centuries the papacy and the feudal lords had continuous conflicts. In the Middle Ages it has a new flourishing port at the mouth of the Fiora river, where the boast loaded freight, especially grain.
The area was unhealthy and in 1421 Pope Martin V, interested in maintaining actively the lifestyle of the pastures, issued a bull in favor of the re-population of the area.
From this moment Montalto became the centre in an agro-pastoral system of stock transfer. Malaria and harsh living conditions of the inhabitants made constant dangers to the population. So there neede to be continuous migration from the Apennines and Corsica to avert the possibility of reduced population.
From 1537 to 1649 it was part of the Duchy of Castro, fiefdom created by Pope Paul III Farnese for his son Pierluigi and when Castro was razed in 1649, the city, even Montalto returned to be part of the Papal State, to which belonged until 1870.
Since the eighteenth century attempts were made on several occasions to rehabilitate the marshy countryside and eradicate malaria, but the operation was successful only after the war with the creation of ‘Ente Maremma.