Until recently, the late-antique castellum of Can Blai (also known as Can Pins) has not received the attention it deserves. Located in Sant Ferran de ses Roques in the centre of the small Mediterranean island of Formentera (Balearic Islands) (fig. 1), the fort was built at the highest (25 m asl) and narrowest point of the isthmus that joins the two major areas of higher ground, Puig Guillem on the north (107 m asl) and La Mola in the south (192 m asl). The fort lies c.600 m from the E shore and c.900 m from the W shore. In 1975, the Swedish resident R. Sternberg mentioned its existence to the second-named author, here, who was then director of the Archaeological Museum of Ibiza and Formentera. Fernández undertook archaeological investigations (1979, 1980) which documented the site and the form of the fort. The fieldwork did not result in full reports, but it was mentioned in a general publication on this island and in accounts of the heritage of the Pityusic Islands.