The twin cities of LaSalle and Peru developed in close connection with the Illinois River and the Illinois and Michigan Canal. Jacques Marquette and Louis Jolliet passed through the area on the Illinois River in 1673 on their way to Lake Michigan, and Robert Cavelier, Sieur de LaSalle, came through in 1680 and again in 1682-83. His lieutenant Henri de Tonti erected Fort St. Louis at Starved Rock to the east, now a state park. Jolliet had first noted the desirability of a canal linking Lake Michigan to the Mississippi by way of the Illinois. In 1825 the Illinois and Michigan Canal Association was incorporated, and in 1836 the legislature passed the Internal Improvement Act, which included a provision for a north-south railroad through Illinois. The convergence of these transportation routes encouraged further settlement in the area. Peru, organized in 1834, was incorporated in 1838. Activity eventually shifted to LaSalle because the canal's boat basin and the railroad routes were ultimately located there. Although settled as early as 1830, LaSalle was not incorporated until 1852. Construction of the canal began in 1836 and was completed in 1848. Extending from the Chicago River to LaSalle-Peru, it served as an important trade link for thirty years. Two railroads completed to LaSalle in the 1850s eventually surpassed the canal in importance, and the twin cities gradually shifted their focus from transportation to mining and industry.