That portion of the shore of the Adriatic which lies between the lake, or rather lagune, of Commachio and the lagunes of Venice, has undergone considerable alterations since ancient times, as is attested by authors worthy of entire credit, and as is still evidenced by the actual state of the soil in the districts near the coast; but it is impossible now to give any exact detail of the successive progress of these changes, and more especially of their precise measures, during the ages which preceded the twelfth century of our, era.

We are however certain, that the city of Hatria, now called Adria, was formerly situated on the edge of the coast; and by this we attain a known fixed point upon the primitive shore, whence the nearest part of the present coast, at the mouth of the Adige, is at the distance of 25,000 metres ; and it will be seen in the sequel, that the extreme point of the alluvial promontory, formed by the Po, is farther advanced into the sea than the mouth of the Adige by nearly 10,000 metres.