Six miles beyond Santa Marinella is the fortress of Santa Severa, standing on the shore, about a furlong from the high-road. It is a square castle, with a keep at one angle, and a lofty round tower, with machicolated battlements, rising in the centre. To the casual observer, it has nothing to distinguish it from other mediaeval forts; but if examined closely, it will be seen that its walls on the side of Civita Vecchia are based on foundations of far earlier date, formed of massive, irregular, polygonal blocks, neatly fitted together without cement,—precisely similar to the walls of Cora, Segni, Palestrina, Alatri, and other ancient towns in the Latin and Sabine Mountains—in short, a genuine specimen of what is called Pelasgic masonry. This wall may be traced by its foundations, often almost level with the soil, for a considerable distance from the sea, till it turns at right angles, running parallel with the shore, and, after a while, again turns towards the sea—enclosing a quadrangular space several times larger than the present fort, and sufficiently extensive for a small town. This is the site of “the ancient Pyrgi.”

These, and the slight remains on the Puntone del Castrato, are the only specimens of polygonal masonry in this part of Etruria, though such is found on three other sites further north. The strict similarity to the walling of cities south and east of the Tiber, seems to imply a common origin, and an origin not Etruscan.