If the immediate environment of the common man furnished no stimulus to enterprise, neither was it provided by anything beyond his neighborhood. Without a system of monetary exchange, trade was limited to barter or to the purchasing power of purse and belt. A brief journey with merchandise was executed with hazard. Every petty lord exacted toll of those who passed the border of his estate. Many of the occupants of the castles lived by open robbery, and kept men-at-arms, as they kept their falcons, to pounce upon their prey. Not only the goods, the persons also of travellers were regarded as legitimate booty, the victims being held for ransom and often sold as slaves. So enterprising were these robber knights that it is said to have been dangerous for the king to go from Paris to St.-Denis without an army at his back. The armed merchantman rode generally with lance in rest. In towns, says Thierry, “nobles, sword in hand, committed robbery on the burghers, and in turn the burghers committed violence upon the peasants who came to buy or sell at the market of the town.” There was considerable foreign commerce on the Mediterranean. The merchants of Pisa, Genoa, and Venice were in rivalry with those of Byzantium, and with the Saracens who held the ports of Spain and North Africa. But, as what are known as maritime laws were not agreed upon until the thirteenth century, commerce was little more than piracy. The trade vessels were burdened with men for their defence, or for rifling the cargoes of less puissant marauders. The mariner’s compass had been invented, but was not in common use, so that trade was compelled to follow the coast-lines, in perpetual hazard of wreck and robbers. There was no importation of things for common use; the labor and danger of transportation limited the articles of trade to those of rarest value, which became the spoil of the powerful or the purchase of the rich. The ordinary man received no benefit from other neighborhoods than his own, except that the air of heaven was sweetened by its passage over the mountains and seas which separated him from his kind.