Suetonius Caligula 19

He invented besides a new kind of spectacle, such as had never been heard of before. For he made a bridge, of about three miles and a half in length, from Baiae to the mole of Puteoli , ¹ collecting trading vessels from all quarters, mooring them in two rows by their anchors, and spreading earth upon them to form a viaduct, after the fashion of the Appian way. ² This bridge he crossed and recrossed for two days together; the first day mounted on a horse richly caparisoned, wearing on his head a crown of oak leaves, armed with a battle-axe, a Spanish buckler and a sword, and in a cloak made of cloth of gold; the, day following, in the habit of a charioteer, standing in a chariot, drawn by two high-bred horses, having with him a young boy, Darius by name, one of the Parthian hostages, with a cohort of the pretorian guards attending him, and- a party of his friends in ,cars of Gaulish make. ³ Most people, I know, are of opinion, that this bridge was designed by Caius, in imitation of Xerxes, who, to the astonishment of the world, laid a bridge over the Hellespont , which is somewhat narrower than the distance betwixt Baiae and Puteoli . Others, however, thought that he did it to strike terror in Germany and Britain , which he was upon the point of invading, by the fame of some prodigious work. But for myself, when I was a boy, I heard my grandfather say, ⁴ that the reason assigned by some courtiers who were in habits of the greatest intimacy with him, was this; when Tiberius was in some anxiety about the nomination of a successor, and rather inclined to pitch upon his grandson, Thrasyllus the astrologer had assured him, "That Caius would no more be emperor, than he would ride on horseback across the gulf of Baiae ."