But the modern writer, as he compares the geographical position of the capitals of Europe, is tempted to exclaim, _Cherchez le marchand!_ for he perceives that their unknown founders were dominated by two considerations--facilities for commerce and protection from enemies: and before the era of the Roman roadmakers, commerce meant facilities for water carriage. As the early settlers in Britain sailed up the Thames, they must have observed, where the river's bed begins somewhat to narrow, a hill rising from the continuous expanse of marshes from its mouth, easily defended on the east and west by those fortified posts which, in subsequent times, became the Tower of London and Barnard's Castle. If we scan a map of France, we shall see that the group of islands on and around which Paris now stands, lies in the fruitful basin of the Seine, known as the Isle de France, near the convergence of three rivers; for on the east the Marne and the Oise, and on the south the Yonne, discharge their waters into the main stream on its way to the sea. In ancient times the great line of Phoenician, Greek and Roman commerce followed northwards the valleys of the Rhone and of the Saone, whose upper waters are divided from those of the Yonne only by the plateau of Dijon and the calcareous slopes of Burgundy. The Parisii were thus admirably placed for tapping the profitable commerce of north-west Europe, and by the waters of the Eure, lower down the Seine, were able to touch the fertile valley of the Loire. The northern rivers of Gaul were all navigable by the small boats of the early traders, and, in contrast with the impetuous sweep of the Rhone and the Loire in the south and west, flowed with slow and measured stream:[5] they were rarely flooded, and owing to the normally mild winters, still more rarely blocked by ice. Moreover, the Parisian settlement stood near the rich corn-land of La Beauce, and to the north-east, over the open plain of La Valois, lay the way to Flanders. It was one of the river stations on the line of the Phoenician traders in tin, that most precious and rare of ancient metals, between Marseilles and Britain, and in the early Middle Ages became, with Lyons and Beaucaire, one of the chief fairs of that historic trade route which the main lines of railway traffic still follow to-day. The island now known as the Cité, which the founders of Paris chose for their stronghold, was the largest of the group which lay involved in the many windings of the Seine, and was embraced by a natural moat of deep waters. To north and south lay hills, marshes and forests, and all combined to give it a position equally adapted for defence and for commerce. [Illustration: THE CITÉ.] [Illustration: POINT DU JOUR.]