The ancient Castrum et Oppidum Petrae owes its name to the massive castle standing on an outcrop of rock over the sea. The Castrum Petrae was occupied first by the Lombards in 641, then by the Franks (and in the tenth century it was victim of many of the Saracen invasions). In the Middle Ages it passed to the Bishop of Albenga, who, using the foundations of the ancient fortress, erected the castle which later became his residence.
In 1395 Pope Urban VI ceded it to the Republic of Genoa, who erected it to the Podestà; in 1419 it was occupied by the Marquis Del Carretto and then returned to the Bishop of Albenga in 1528. During the Napoleonic era, Pietra Ligure remained property of the Republic of Genoa. The city had meanwhile developed its maritime abilities and shipbuilding; by 1738 Genoa had promoted the development of the economy of the town, leading to its urban expansion with the construction of the Marina District. Since 1815, the year of the annexation to the Kingdom of Sardinia, and throughout the century, the activities linked to the sea were further expanded. During the Second World War the old neighborhood of the “Ajetta” was destroyed by the Allied bombings; on 29th June 1944, trying to hit the railway bridge, a bombing caused six victims. The neighborhood was rebuilt in the ’60s.
The Maremola stream was restless. Its name comes from the “fen”, the swamp that had been created in the lowlands at its left and into which flowed even brackish water. An unhealthy area, therefore, whose reclamation was essential, as well as the construction of levees that could hold the river in its bed: these were the concerns that plagued the ancient Pietresi, as we can read in the chronicles of 1600. And from the chronicles of the past centuries can be derived the history of the bridges and, above all, the floods that damaged it and brought it down more than once. The Maremola overflowed in April 1604, in 1693, in November 1738, in September 1743 and in the October of the following year. In 1756 the wooden bridge was eventually dragged to the sea. More floods followed until 1780, when the bridge was built – a “humpback” and the “chapel” – and this would last until 1933 (the year of a disastrous flood that claimed the lives of four people). The bridge was not suited to the vehicles that forded the river. To get to the bridge on the Via Nazionale, with its access to the country in the direction of Via Matteotti, you would have to wait until 1862. Two major floods took place in November 1886 and in September 1900, when the new stone bridge collapsed on the provincial road, then was replaced with a iron that was bombed in 1944. Currently they are working on the construction of a new, large deck that will revolutionize the viability and the links between the west and east of the town.