Joliet was the leader of the party, and he was accompanied, as was the custom in French expeditions into unknown countries, by a missionary, who in this case was James Marquette, a Jesuit priest. Both were young men, Joliet twenty-eight years of age and Marquette thirty-six. The expedition had been authorized by the French Government, the purpose being to penetrate the western wilderness in an endeavor to reach the "Great River," of which so much had been heard from wandering tribes of Indians, and to find the direction of its flow. Many conjectures were made by the men of that time as to the course of this river and where it reached the sea, some believing that it emptied into the "Sea of Virginia," others that it flowed into the Gulf of Mexico, and still others that it discharged its waters into the "Vermilion Sea," that is, the Gulf of California; and if the latter conjecture should prove to be correct a passage might thus be opened to China and India. In the event of such a discovery being made, great honor would naturally accrue to its projectors. The instructions to undertake such an expedition came from Colbert, the minister of Louis XIV, who wrote in 1672 to Talon, the Intendant at Quebec, that an effort should be made "to reach the sea"; that is, to discover and explore the "Great River" and solve the mystery of its outlet. Father Dablon, in the _Jesuit Relations_, thus wrote of the enterprise about to be undertaken: "The Count Frontenac, our Governor, and Monsieur Talon, then our Intendant, recognizing the importance of this discovery, ... appointed for this undertaking Sieur Joliet, whom they considered very fit for so great an enterprise; and they were well pleased that Father Marquette should be of the party." The expedition was accordingly organized, and started from the Mission of St. Ignace on the 17th of May, 1673. In due course the party reached the mouth of the Fox River (of Wisconsin), at the head of Green Bay. From this point the party passed up the Fox and soon after crossed the portage into the Wisconsin River. They were now far beyond the farthest point reached by any previous explorers. On the 17th of June the explorers paddled their canoes out on to the broad bosom of the Mississippi. Marquette wrote in his journal that when he beheld the great river it was "with a joy that I cannot express." It was while carrying out the purposes of this expedition that the explorers passed through the Chicago River from the west. They had reached the Mississippi as they had planned to do, had floated down its current as far as the mouth of the Arkansas, and on the way back had ascended the Illinois and Desplaines rivers, made a portage into the Chicago River, and, passing out on Lake Michigan, pursued their journey to the point on Green Bay at the mouth of the Fox River from which they had started at the beginning of June, after an absence on the journey of almost four months.