Puteoli (now Pozzuoli) was a major Roman port. It was sheltered by the most famous arched breakwater. This breakwater was buried under the modern breakwater (!) but it was still visible in the 19th c. and known as “Molo Caligoliano”:
It can be seen from the dates of these pictures that the structure was gradually destroyed.
Paolo Antonio PAOLI, provided the dimensions of the ancient arched structure in his “Antichita di Pozzuoli” in 1768 (with some later editions).
The drawing shows 15 pilae (including 2 supposed pilae). The largest pilae of ca. 15 x 15 m are at the offshore end of the structure. The nearshore pila is somewhat smaller: ca. 8 x 12 m. The opening between adjacent pilae varies from 0.7 to 1.0 pila width, which is close to the values found for the arched breakwaters of Portus Iulius and Misenum.