The chief exports of Gaul appear to have been gold, silver, and iron from its own mines; linens from every part of the country; corn and cheese of superior quality; with excellent salt pork, and tartan cloths. Burdigala (Bordeaux,) on the Garonne, was its chief port on the west, and on the north the Portus Itius (by some supposed to be Wissant, near Cape Grisnez, but more probably Boulogne). At this port, called afterwards Gessoriacum,[311] and whence Cæsar sailed for Britain, was the lighthouse constructed by Caligula, some remains of which are said to have existed in the early part of the seventeenth century. This tower, or Pharos, the first lighthouse on record for any part of the coasts of the North Sea or English Channel, stood upon the promontory or cliff which commanded the port. Of an octagonal form (if Bucherius is right in supposing the building he has drawn to be the remains of Caligula’s structure), it was twenty-five feet in breadth, and the circumference of the whole at the base two hundred feet. It had twelve storeys or spaces for galleries, rising above each other. Each storey diminished in diameter as you ascended, and on the top of the tower a fire was kindled every evening at sunset, and served as the beacon light for the guidance of mariners. [Sidenote: The shipping described by Tacitus.] [Sidenote: Rhodians.] Tacitus[312] has preserved a description of the expedition of Germanicus, but his “Annals” throw little light upon the state of that portion of the Roman navy which assisted in the conquest of Germany, and frequented the northern seas about the period when the first lighthouse was erected in the English Channel. Indeed his description very imperfectly represents either the vessels or seamen of those maritime nations, who, becoming subject to Rome, largely aided her alike in her naval and in her commercial victories. Of these none have left a more lasting record of their existence as a maritime people than the Rhodians. Alike celebrated for their skill as navigators, and their honesty and shrewdness as merchants, they excelled all others as jurists. Their laws relating to navigation were introduced into the Roman code, and formed the groundwork of maritime jurisprudence throughout the civilized world. Colonized, no doubt, by some of the more civilized nations of Western Asia, and probably by the Phœnicians, the Rhodians from their position, in a small island and on the great highway of commerce, as well as from their skill in astronomy and in navigation, soon took a prominent part among nations more populous and powerful than themselves. Accessible to all the surrounding naval powers, and deriving their chief commercial wealth from their trade with Egypt, the Rhodians from the first made it their business to keep the police of the surrounding seas; and having punished the pirates who then infested the Mediterranean with exemplary severity, pursued their trade as merchant navigators with equal security and success.