The San Marco lock was built in the 1830s, to allow the confluence of the Ronco River and the Montone River to be diverted about 3 km south of the city with a stretch of artificial bed (the United Rivers); this was the first of numerous interventions as part of the massive diversion work of the United Rivers, which during the 1700s changed the hydrographic structure in the Ravenna area.
From the Chiusa di San Marco an artificial canal was built, dug in the direction of the Panfilio: the ancient canal port (which fell into disuse following this intervention), where the confluence of the two rivers is still visible. These works had significant positive repercussions on the events in the city of Ravenna. The construction of the San Marco lock was thus completed in parallel with the excavation works of the riverbed of the United Rivers.
The functions of the sluice are manifold; in addition to regulating the lack of height difference existing between the two riverbeds, it is to support the diversion of water for the town's mills.