The inland routes which required the least capital to utilize in a primitive way were the rivers. Here the chief obstacle was the current. In the early nineteenth century long lines of rafts, flat-boats and "arks" might be seen floating down the Connecticut, the Hudson, the Susquehanna and the Potomac. There were 2,800 miles of rivers tributary to the Atlantic seaboard which were navigable, or which needed only to be cleared of snags and rocks to render them available for use by small craft. It was estimated that on the eastern slope there were about 25,000 miles of streams which might be utilized by the construction of locks and canals. In the Mississippi valley there were 14,000 miles of navigable rivers, and about 75,000 more which were considered possibilities. But with a three or four-mile current it was impracticable to row, pole or warp a boat and cargo upstream for a long distance. The result was that along those streams which nature had provided as highways the producer first built his boat out of the timbers of the forest, then loaded it with the produce of his farm or mill, and floated down stream to market. Upon reaching his destination, he abandoned his craft and returned by stage or on foot. This was indeed an expensive process--expensive in time, expensive in funds and expensive in human effort. It was an expense of production, however, and one which did not require capitalization. It was not until 1807 that the steamboat became a commercial success. At this time New York was becoming well settled, and as the Hudson was a natural highway a boat which could drive against wind and stream had every promise of success. Robert Fulton, who had been interested in the problem of steam navigation since 1802, returned from Europe after several years of investigation, and brought back one of Watt's engines. He obtained the financial co-operation of Chancellor Livingston, and together they obtained a monopoly of steam navigation in New York waters. A boat was fitted with the Watt engine, and a successful trip was made from New York to Albany and return. The route yielded large profits from the start, and other boats were built. By 1813 six boats were doing a profitable business on the Hudson. The success of Fulton and Livingston proved attractive to others. Crowded out of New York's waters by the monopoly, John Stevens, in 1809, took a steamboat around from Hoboken into the Delaware. The Phoenix now found business so good in those waters where Fitch had failed that it was soon followed by two other boats. Soon the whole Atlantic seaboard, including the St. Lawrence, was supplied with steam craft.