Pliny (NH, 16.20) and Suetonius (Claudius, 20.3) have told us the story of the great ship that Caligula had built for the transport of the obelisk now in the Vatican, which was later sunk by Claudius after being filled with pozzolana. It was reused as the foundation of the lighthouse of the new seaport he was building north of Ostia. This exceptionally large vessel would have had a deadweight of 1,300 tons and would have transported, in addition to the obelisk, 130,000 modii of lentils.Otello Testaguzza (Portus. Illustrazione dei porti di Claudio e Traiano e della città di Porto a Fiumicino, Rome, 1970) attempted to recognize the traces of Caligula's ship and some other smaller boats in the concrete of the northern pier of the port of Claudius at Fiumicino, however, his identifications do not correspond to the archaeological reality and the location of Caligula's ship remains, for the moment, hypothetical. In recent years, numerous underwater excavations carried out at multiple sites in Dalmatia attest to the systematic reuse of boats as building materials, a practice widely used in the Mediterranean during Antiquity and later periods, as testified by both historical documents and archaeological finds. The sites of Caška on the island of Pag and Kaštel Sućurac near Split offer remarkable examples of boats sunk voluntarily after being filled with stones. The examination of these wharves not only tells us about new types of harbour constructions, but provides valuable data on the characteristics of the original ships.