In our last memoir on Navigation and Commerce, we brought the maritime history of Greece down to the period of the Trojan war: on the present occasion we shall extend our inquiries to the invasion of Greece by Xerxes, and the events which led to the defeat of that formidable invader. The first object which engaged the attention of Xerxes on his accession to the throne of Persia, was the reduction of Egypt, which having accomplished, he determined to carry his arms into Greece, to revenge the insult of the burning of Sardis, and wipe away the disgrace of the defeat of Marathon. Four years were employed in preparations, and an army was collected, the most numerous that has ever appeared in the world. The naval forces of the Persian monarch were on a scale of equal magnitude. In a former war the Persian fleet had suffered shipwreck in attempting to double the promontory of Mount Athos; and to prevent the repetition of a similar disaster, Xerxes caused a canal to be cut, navigable for the largest gallies, through the isthmus which joins Athos to the continent of Thrace. Another magnificent work which he effected, was to build two bridges of boats, of the length of seven furlongs, over the Hellespont; and some idea may be formed of the prodigious numbers of his army, when it is related, that seven days and nights, unremittingly employed, were consumed in passing these bridges.