The Nen from Northampton to Wisbech is "navigable with difficulty"--where the water is sufficient at all--by barges of the smallest size; but sometimes navigation even by these barges is impracticable for weeks together in certain parts of the river. Between Northampton and Peterborough the course of the Nen is extremely tortuous. "It would," says the report, "take a barge nearly three days to travel the sixty-one miles by water, while the railway can carry goods from Northampton to Peterborough in two hours." It is thus evident that rivers, whether navigable naturally or rendered so by art, must be regarded as water highways possessed of considerable disadvantages and drawbacks in respect to inland traffic when they are on the scale and of the type found in England. Dependent on the forces of Nature--ever active and ever changing--rivers must needs be the exact opposite of the fixed and constant railway line unless those forces can be effectually controlled under conditions physically practicable and not too costly. "Rivers," says L. F. Vernon-Harcourt, in his book on "Rivers and Canals," "are not always suitable for navigation, in their {157}natural condition, even in the lower portions of their course; and, owing to the continual changes taking place in their channels and at their outlets, they are liable to deteriorate if left to themselves." Left to themselves the English rivers, like the Roman and the British roads, were for a thousand years after the departure of the Romans, and the liability to deteriorate may well have shown itself during this period, before even the earliest of the River Improvement Acts was passed; though the deterioration due to the ceaseless operations of Nature may obviously continue in spite of all Acts of Parliament, and notwithstanding a great expenditure of money. The fate that has overtaken so many English rivers which once counted as highways of commerce may be compared with the fate that, also through the operation mainly of natural causes, has overtaken many of our once flourishing sea ports. When, in the thirteenth century, Liverpool was raised to the rank of a free borough, there were between thirty and forty places which, whether situated on the coast or some distance inland (as in the case of York), were counted as seaports. Their order of importance at that time is shown by the following table (taken from Baines's "History of Liverpool"), which gives the taxation then levied on each; though the amounts stated should be multiplied by fifteen to ascertain their equivalent in the money of to-day:--