Torre Pietra has a square plan, 11.50 m wide externally; the upstream side faces the Margherita di Savoia saltpans. An external staircase with a single ramp perpendicular to the upstream sideemerges from the floor and leads to the access to the first floor while the north side faces the sea.
It was built around 1537, at the behest of the viceroy Don Pedro de Toledo. It is also called the “Torre della Punta della Pietra” (Tower of the tip of the stone) because in ancient times it extended into the sea for about 4 km, across a promontory known as San Nicolao de Petra, which over time slowly sank due to marine erosion. Torre Pietra is part of a large and integrated coastal defensive system of fortified towers that were used for sightings of the Turks along the Adriatic, also following the disastrous events in Otranto in 1480.
Originally the first floor was accessed from the wall with a retractable ladder; loopholes on the opposite side looked out at the sea and the other sides for a wide range.
This stretch of coast has always been historically very important: first with San Nicolao de Petra, patron saint of Barletta then, once the coastal erosion began (13th century), the medieval center, also home to a monastery, was moved towards the interior, forcing the tower to be moved where we see it today, and where it is still subject to the phenomena of coastal erosion that affect this stretch of the Apulian coast.
Torre Pietra, like the other coastal defensive towers of the Spanish viceroyalty, had a mixed function: they served as a sighting and signaling of dangers from the Adriatic, as fortification buildings, as customs posts and for controlling the waters of Lake Salpi. In fact, the tower was also used over the years as a technical office during the reclamation of Salpi and subsequently as a Brigade Command of the Guardia di Finanza, no longer operational.
Along the beach and in the first stretch of sea, at a shallow depth, it is still possible to see archaeological remains of a wall structure, mentioned by Vitruvius in reference to the refoundation of Salapia during the Roman age. A few steps from the tower, around 1770, a small church was built, dedicated to the cult of San Michele Arcangelo. There are also two other buildings, now in ruins, which housed a tavern and a salting house for eels, which were fished in Lake Salpi as it still happens in the nearby lakes of Lesina and Varano. Later, at the end of the nineteenth century, with the transformation of the lake into Salina Regia, some small buildings were built for the residence of the Salinieri, in charge of managing the water flows in the salination tanks, essential for the production of salt.