The lock, the derivation and the relative canal were built in an unspecified period to feed the mills that operated in the stretch between San Varano and the Romiti.
The first news on the existence of the Ladino lock (also known as San Martino) dates back to December 1436 when the commander of the Castrocaro garrison noticed, during an inspection on the border with the territory of Forlì that part of the Faragana lock had been built on land belonging to the Castrocarese jurisdiction and ordered its demolition. The mills were no longer able to grind and the people of Forlì unsuccessfully claimed the reconstruction of the building at the expense of the Florentine Republic.
In 1442 Antonio Ordelaffi, lord of Forlì, accompanied by some heads of the magistracy of the city, met with the commissioner Captain Jacopo Ventura to agree on the construction of a new dam in order to re-introduce the water into the canal. On 29 January 1919 the Cartiera Romagnola, which took over the ownership of the Unione dei Molini di Ravaldino, denounced the cessation of the activity of most of the mills and asked to be able to use the derivation for the production of electricity by exploiting the strength that the water acquired. from the point where the canal detaches from the road and descends towards the river through a short but marked difference in height.
The milling activity continued only for the San Varano mill (Gualchiera) which used the water of the canal until 1996, the year it ceased to operate.
Today the Ladino lock is a concrete construction with brick masonry shoulders and an upper arch 66 meters long which generates a difference in height of the water surface of 9 meters.
A small plant for the production of electricity was built nearby.
In the 1950s and 1960s, the large space created in front of the lock and its water mirror were the destination in the summer months for many groups who gathered here to sunbathe and swim. Today no one dares to get wet, also in consideration of the poor quality of the water, but from time to time you can see fishermen who patiently wait for some fish to bite and some walkers who stop to take a breath and to admire a place that is certainly interesting and also suggestive.