The castellum of Can Blai is a small late-Imperial Roman fortification, built between the end of the 3rd century and the beginning of the 4th century AD. Square in plan and measuring about 40 metres per side, it features five rectangular, slightly trapezoidal towers projecting outward. Excavations carried out in the 1970s and 1980s concluded that it was an unfinished structure, with hardly any signs of occupation. It was declared a Site of Cultural Interest in 1994, and today the foundations of its walls and towers survive. It stands at the highest point of the isthmus connecting La Mola with the rest of the island, beside the road from La Savina to La Mola (km 10). The best time to visit is early in the morning or late in the day, when the raking light brings out the ruins.