The limestone headland that closes the eastern arm of the Gulf of Cagliari is named for a battle no chronicle records. Local tradition holds that the Devil, defeated by the Archangel Michael above these waters, fell and left his saddle behind. Geologists give a plainer account: the Sella del Diavolo is Miocene limestone, roughly 130 metres high, layered with the shells of a warm shallow sea that covered southern Sardinia some fifteen million years ago. The promontory has always been a gate rather than a wall. Phoenician sailors used it as a bearing when approaching the lagoon settlement that became Karalis. Rome built cisterns on its ridge. A Byzantine watchtower, later rebuilt by the Pisans and again by the Spanish, marked the sightline that any cagliari sailing tour still follows out of Marina Piccola. Ruins of the Torre del Prezzemolo remain on the summit, weathered but legible. Below them, the sea floor drops in terraces of posidonia meadow, the seagrass that keeps Sardinian water its particular unclouded blue. What distinguishes this coast is compression. Within roughly six nautical miles of the Port of Cagliari a sailboat passes Poetto's eight-kilometre sand shelf, the Molentargius saltpans where flamingos feed, the cliffs at Calamosca with their Spanish signal tower, and the sheltered inlets of Cala Fighera and Cala Regina. Few Mediterranean capitals put a working harbour, a nature reserve and a snorkeling cove inside the same afternoon's sailing. Sail has a long local logic here. The gulf sits in the path of the mistral and the scirocco, and Sardinian rigs were built to work both. Modern sloops and gozzi under canvas cross the bay quietly, which matters where dolphins and grouper are common and engine noise carries. The Gulf itself is public water — entry costs 0 EUR, and the coastline is open daily from 09:00 to 21:00 — while the vessels that cross it are private commercial services with their own fares. The headland is protected as a natural monument, and its coves resist land access almost entirely; the coastal path stops where the cliff begins. Approach from the water and the sequence reverses. Cagliari's tiered old town, the Castello bastions, the yellow limestone of the Bastione di Saint Remy all recede into one silhouette. A well-run cagliari sailing tour trades the postcard view of the city for the view the city was built to command.