The Astura Tower, at the mouth of the river Astura, is built on the remains of a fishing pond in a Roman villa and is recognized as one of the two arms of the Roman port. Pliny describes Astura like an island, and you can recognize the remains of a bridge that connected the island to the mainland. In some Astura records it is cited as one of the Appian Way Stations. The Romans had built a port and an imperial palace whose ruins remain. Probably Augustus, Tiberius and Caligula stayed there. The construction of the tower by Frangipane to defend the harbor from Saracen raids dates back to 1193. In 1268 Astura Tower was captured by the young Conradin, grandson of Frederick II. After being a fiefdom of the Castani and Orsini, in 1426 Astura passed to the Colonna, who, in the mid-sixteenth century, rebuilt the castle, giving it the current Renaissance appearance. For the German traveller Ferdinand Gregorovius, who was in Nettuno in mid-nineteenth century, Astura Tower "is the star of Romanticism, it is the tower of the German poets in Italy" and should be declared a German national property.