In mediaeval times rivers were the veins of the body politic as well as economic.
Boundaries between states or shires, they were crossed by fords which became
the sites of towns, or by bridges which were often points of battle. Upon rivers
the people of that time depended for food, power and transport.
In our day fish are caught in the sea and brought to us by rail and lorry; only
the angler still thinks fresh-water fish important, and pollution of rivers drives
him into smaller and smaller reaches in which to practise his sport. But in earlier
times, when sea fish were eaten only by those who lived on the sea coast, when
meat was obtainable only for part of the year, and when fasts were frequent and
universally practised, river fish played an important part in the national life.
Every abbey and great man's house had its fish pond, and across the rivers great
and small stretched the fish weirs, usually made of stakes and nets or basket-
work. Between the owners of the fisheries and the bargemaster who needed an
unimpeded passage continuous war was fought, till the importance of fresh-
water fish lessened as the practice of fasting ceased to be universal, as meat be-
came available all the year round, and as the transport of sea fish inland became
practicable.
Rivers were also the most important source of power. Every stream had its
mills, not only for grinding corn, but for all the other industrial processes of the
time, such as fulling* cloth or driving the hammers of ironworks. Placed down
the bank wherever a head of water could be got, these mills were to be found on
the tiny stream that ran through a village, or on the bigger river that was also
used for navigation. An artificial cut was made from the river to bring the water
at proper height to the water-wheel, and, in order to make sure of a supply of
water at all seasons, the mill-owner usually built a weir across the river to hold
back the water and so form an artificial reservoir. If the river were navigable, the
centre of such a weir was made of planks held vertically by cross beams so that
they could be removed when it was necessary to pass a barge, or was fitted with
a single pair of gates. Such weirs were called staunches or flash-locks; they did
not disappear from the bigger rivers till present times, and may still be seen in
the Fens.
* Cleansing and thickening.