Omnes kydelli de cetero deponantur penitus de Thamisia, et de Medewaye, et per totam Angliam, nisi per costeram maris.
All fish-weirs are in future to be entirely removed from the Thames and the Medway, and throughout the whole of England, except on the sea-coast.
Most of the clauses of Magna Carta aimed to remedy abuses committed by the king and his agents. Clause 33 is an exception, in that it demanded that the king use his powers for the benefit of his subjects, or at any rate a particular group of them, without suggesting that he was himself responsible for the grievance in question. Indeed, both Richard I and John himself had already tried to resolve what proved to be a recurring problem. The problem was the fish-weir, which was proliferating in the Thames, and probably in other rivers as well, to such an extent that it was becoming a serious hindrance to navigation, and so to trade. There had been traps to catch fish in English waters for centuries, but a new form seems to have been introduced from the Continent in the late twelfth century, larger and heavier than its predecessors. Made of poles and beams, and sometimes with a stone base, it was a substantial V-shaped structure, which worked by guiding fish that swam into its arms towards a net or basket at its centre. London needed fish, both to feed its growing population and to meet the needs of those who observed the numerous fast-days of the Church by eating fish instead of meat. But it needed to keep its waters clear as well, so that shipping could move safely up and down the Thames, and the new fish-traps clearly proved a serious obstacle. The total removal of fish-weirs, from the Thames and Medway (downstream from London, on the northern shore of Kent), and also from all other rivers, was ordered in response. A concluding phrase, excepting coastal fish-weirs from the prohibition, was probably added in recognition that such devices were less likely to hinder the movement of boats than weirs in rivers, but it may also have been intended to benefit the ecclesiastical and secular lords who were the likeliest owners of fish-traps which were set up along the shoreline.
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