The bridge of ships at Baiae (c. AD 39)

Caligula had a bridge built of merchant ships between Baiae and Puteoli, about five kilometers long, and rode across it on two days: on the first on horseback, in a wreath of oak leaves and a golden cloak, on the second in a chariot (Suetonius, Caligula 19; Dio 59.17; Josephus, Antiquities of the Jews 19.1).

The bridge itself existed. Its purpose is disputed: rivalry with Xerxes, a show of strength before Germania and Britain, or a response to the prophecy of the astrologer Thrasyllus. Dio links its construction with a famine in Italy.